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- abyss, abysm
a bottomless gulf or pit - abyssal zone
the deep sea (2000 meters or more) where there is no light - achondrite
a stony meteor lacking chondrules - acicula
a needlelike part or structure of a plant or animal or crystal - adjunct
something added to another thing but not an essential part of it - aerie, aery, eyrie, eyry
the lofty nest of a bird of prey (such as a hawk or eagle) - aerolite
a stony meteorite consisting of silicate minerals - agent
an active and efficient cause - airborne transmission
a transmission mechanism in the which the infectious agent is spread as an aerosol and usually enters a person through the respiratory tract - air bubble
a bubble of air - alluvial sediment, alluvial deposit, alluvium, alluvion
clay or silt or gravel carried by rushing streams and deposited where the stream slows down - alluvial flat, alluvial plain
a flat resulting from repeated deposits of alluvial material by running water - alp
any high mountain - alpha particle
a positively charged particle that is the nucleus of the helium atom - Alpine glacier, Alpine type of glacier
a glacier that moves down from a high valley - altocumulus, altocumulus cloud
a cumulus cloud at an intermediate altitude of 2 or 3 miles - altostratus, altostratus cloud
a stratus cloud at an intermediate altitude of 2 or 3 miles - ammonite, ammonoid
one of the coiled chambered fossil shells of extinct mollusks - anion
a negatively charged ion - anthill, formicary
a mound of earth made by ants as they dig their nest - antibaryon
the antiparticle of a baryon - antilepton
the antiparticle of a lepton - antimeson
the antiparticle of a meson - antimuon, positive muon
the antiparticle of a muon - antineutrino
the antiparticle of a neutrino - antineutron
the antiparticle of a neutron - antiparticle
a particle that has the same mass as another particle but has opposite values for its other properties - antiproton
an unstable negatively charged proton - antiquark
the antiparticle of a quark - antitauon, tau-plus particle
an antilepton of very great mass - aperture
a natural opening in something - aquifer
underground bed or layer yielding ground water for wells and springs etc - archeological remains
a relic that has been excavated from the soil - archipelago
a group of many islands in a large body of water - arete
a sharp narrow ridge found in rugged mountains - arroyo
a stream or brook - raise, rise, ascent, climb, upgrade, acclivity
an upward slope or grade (as in a road) - asterism
(astronomy) a cluster of stars (or a small constellation) - asteroid
any of numerous small celestial bodies composed of rock and metal that move around the sun (mainly between the orbits of Mars and Jupiter) - asthenosphere
the lower layer of the crust - atmosphere
the envelope of gases surrounding any celestial body - atoll
an island consisting of a circular coral reef surrounding a lagoon - backwater
a body of water that was created by a flood or tide or by being held or forced back by a dam - badlands
deeply eroded barren land - bank
a long ridge or pile - bank
sloping land (especially the slope beside a body of water) - bank, camber, cant
a slope in the turn of a road or track - bar
a submerged (or partly submerged) ridge in a river or along a shore - barbecue pit
a pit where wood or charcoal is burned to make a bed of hot coals suitable for barbecuing meat - barrier
anything serving to maintain separation by obstructing vision or access - barrier island
a long narrow sandy island (wider than a reef) running parallel to the shore - barrier reef
a long coral reef near and parallel to the shore - baryon, heavy particle
any of the elementary particles having a mass equal to or greater than that of a proton and that participate in strong interactions - base
the bottom or lowest part - basin
a natural depression in the surface of the land often with a lake at the bottom of it - bay, embayment
an indentation of a shoreline larger than a cove but smaller than a gulf - bayou
a swampy arm or slow-moving outlet of a lake (term used mainly in Mississippi and Louisiana) - beach
an area of sand sloping down to the water of a sea or lake - beachfront
a strip of land running along a beach - bed, bottom
a depression forming the ground under a body of water - bed
(geology) a stratum of rock (especially sedimentary rock) - bedrock
solid unweathered rock lying beneath surface deposits of soil - beehive, hive
a structure that provides a natural habitation for bees - honeycomb
a structure of small hexagonal cells constructed from beeswax by bees and used to store honey and larvae - belay
something to which a mountain climber's rope can be secured - ben
a mountain or tall hill - berm
a narrow ledge or shelf typically at the top or bottom of a slope - beta particle
a high-speed electron or positron emitted in the decay of a radioactive isotope - bight
a broad bay formed by an indentation in the shoreline - billabong
a branch of a river made by water flowing from the main stream only when the water level is high - billabong
a stagnant pool of water in the bed of a stream that flows intermittently - binary, binary star, double star
a system of two stars that revolve around each other under their mutual gravitation - biological agent, biohazard
any bacterium or virus or toxin that could be used in biological warfare - bird's nest, bird nest, birdnest
nest where birds lay their eggs and hatch their young - chip, scrap, bit, fleck, flake
a small fragment of something broken off from the whole - black body, blackbody, full radiator
a hypothetical object capable of absorbing all the electromagnetic radiation falling on it - black hole
a region of space resulting from the collapse of a star - bladder stone, cystolith
a calculus formed in the bladder - blade
something long and thin resembling a blade of grass - blanket, mantle
anything that covers - blood-brain barrier
a mechanism that creates a barrier between brain tissues and circulating blood - blue, blue sky, blue air, wild blue yonder
the sky as viewed during daylight - bluff
a high steep bank (usually formed by river erosion) - b-meson
exceedingly short-lived meson - body
an individual 3-dimensional object that has mass and that is distinguishable from other objects - water, body of water
the part of the earth's surface covered with water (such as a river or lake or ocean) - bog, peat bog
wet spongy ground of decomposing vegetation - bolt-hole
a hole through which an animal may bolt when pursued into its burrow or den - bonanza
an especially rich vein of precious ore - borrow pit
a pit created to provide earth that can be used as fill at another site - boson
any particle that obeys Bose-Einstein statistics but not the Pauli exclusion principle - bottom, bottomland
low-lying alluvial land near a river - bottom quark, beauty quark
a quark with a charge of -1/3 and a mass about 10,000 times that of an electron - boulder, bowlder
a large smooth mass of rock detached from its place of origin - brae
a slope or hillside - branch
a stream or river connected to a larger one - branched chain
an open chain of atoms with one or more side chains attached to it - breach
an opening (especially a gap in a dike or fortification) - brickbat
a fragment of brick used as a weapon - brook, creek
a natural stream of water smaller than a river (and often a tributary of a river) - brooklet
a small brook - bubble
a hollow globule of gas (e.g., air or carbon dioxide) - bullet hole
a hole made by a bullet passing through it - tunnel, burrow
a hole made by an animal, usually for shelter - butte
a hill that rises abruptly from the surrounding region - concretion, calculus
a hard lump produced by the concretion of mineral salts - caldera
a large crater caused by the violent explosion of a volcano that collapses into a depression - canal
(astronomy) an indistinct surface feature of Mars once thought to be a system of channels - canon, canyon
a ravine formed by a river in an area with little rainfall - canyonside
the steeply sloping side of a canyon - cape, ness
a strip of land projecting into a body of water - carpet
a natural object that resembles or suggests a carpet - cascade
a small waterfall or series of small waterfalls - cataract
a large waterfall - catch
anything that is caught (especially if it is worth catching) - cation
a positively charged ion - cave
a geological formation consisting of an underground enclosure with access from the surface of the ground or from the sea - cavern
a large cave or a large chamber in a cave - cavern
any large dark enclosed space - celestial body, heavenly body
natural objects visible in the sky - chain, chemical chain
(chemistry) a series of linked atoms (generally in an organic molecule) - channel
a deep and relatively narrow body of water (as in a river or a harbor or a strait linking two larger bodies) that allows the best passage for vessels - chap
a crack in a lip caused usually by cold - charm quark
a quark with an electric charge of +2/3 and a mass 2900 times that of an electron and a charm of +1 - chasm
a deep opening in the earth's surface - chink
a narrow opening as e.g. between planks in a wall - chip, cow chip, cow dung, buffalo chip
a piece of dried bovine dung - Chiron
an asteroid discovered in 1977 - chondrite
a rock of meteoric origin containing chondrules - chondrule
small granule (of e.g. chrysolite) found in some meteoric rocks - chromosphere
a gaseous layer of the sun's atmosphere (extending from the photosphere to the corona) that is visible during a total eclipse of the sun - clinker, cinder
a fragment of incombustible matter left after a wood or coal or charcoal fire - cirque, corrie, cwm
a steep-walled semicircular basin in a mountain - cirrocumulus, cirrocumulus cloud
a cloud at a high altitude consisting of a series of regularly arranged small clouds resembling ripples - cirrostratus, cirrostratus cloud
a thin uniform layer of hazy cloud at high altitude - cirrus, cirrus cloud
a wispy white cloud (usually of fine ice crystals) at a high altitude (4 to 8 miles) - clast
(geology) a constituent fragment of a clastic rock - clastic rock
(geology) a rock composed of broken pieces of older rocks - drop, drop-off, cliff
a steep high face of rock - ring, closed chain
(chemistry) a chain of atoms in a molecule that forms a closed loop - closed universe
(cosmology) a universe that is spatially closed and in which there is sufficient matter to halt the expansion that began with the big bang - cloud
a visible mass of water or ice particles suspended at a considerable altitude - cloud bank
a layer of clouds seen from a distance - coast
a slope down which sleds may coast - coastal plain
a plain adjacent to a coast - coastland
land in a coastal area - coffee grounds
the dregs remaining after brewing coffee - gap, col
a pass between mountain peaks - collector
a crater that has collected cosmic material hitting the earth - collision course
a course of a moving object that will lead to a collision if it continues unchanged - coma
(astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet - comet
(astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit - commemorative
an object (such as a coin or postage stamp) made to mark an event or honor a person - consolidation
something that has consolidated into a compact mass - constellation
a configuration of stars as seen from the earth - continent
one of the large landmasses of the earth - continental glacier
a glacier that spreads out from a central mass of ice - continental shelf
the relatively shallow (up to 200 meters) seabed surrounding a continent - continental slope, bathyal zone, bathyal district
the steep descent of the seabed from the continental shelf to the abyssal zone - contrail, condensation trail
an artificial cloud created by an aircraft - coprolite
fossil excrement - coprolith, fecalith, faecalith, stercolith
a hard mass of fecal matter - coral reef
a reef consisting of coral consolidated into limestone - core
the central part of the Earth - core
a cylindrical sample of soil or rock obtained with a hollow drill - corner
a projecting part where two sides or edges meet - couple
(physics) something joined by two equal and opposite forces that act along parallel lines - cove
a small inlet - cove
small or narrow cave in the side of a cliff or mountain - covering, cover, natural covering
a natural object that covers or envelops - crack, fissure, cleft, crevice, scissure
a long narrow opening - crag
a steep rugged rock or cliff - cranny
a small opening or crevice (especially in a rock face or wall) - crater
a bowl-shaped depression formed by the impact of a meteorite or bomb - craton
the part of a continent that is stable and forms the central mass of the continent - crevasse
a deep fissure - crust, Earth's crust
the outer layer of the Earth - incrustation, encrustation, crust
a hard outer layer that covers something - crystal, crystallization
a rock formed by the solidification of a substance - crystallite
any of numerous minute rudimentary crystalline bodies of unknown composition found in glassy igneous rock - tillage, farmland, cultivated land, plowland, ploughland, tilled land, tilth
arable land that is worked by plowing and sowing and raising crops - cumulonimbus, cumulonimbus cloud, thundercloud
a dark cloud of great vertical extent charged with electricity - cumulus, cumulus cloud
a globular cloud - curtain
any barrier to communication or vision - cutting
a piece cut off from the main part of something - dale
an open river valley (in a hilly area) - dander
small scales from animal skins or hair or bird feathers that can cause allergic reactions in some people - dandruff
loose scales shed from the scalp - deep
literary term for an ocean - gorge, defile
a narrow pass (especially one between mountains) - dell, dingle
a small wooded hollow - delta
a low triangular area of alluvial deposits where a river divides before entering a larger body of water - delta ray
an electron ejected from matter by ionizing radiation - fall, descent, declination, declension, declivity, decline, downslope
a downward slope or bend - desideratum
something desired as a necessity - deuteron
the nucleus of deuterium - diapir
a domed rock formation where a core of rock has moved upward and pierced through the more brittle overlying strata - diffuse nebula, gaseous nebula
a cluster of stars within an intricate cloud of gas and dust - dipole
a pair of equal and opposite electric charges or magnetic poles separated by a small distance - dipole molecule
a molecule that is a permanent dipole