A geological formation consisting of an underground enclosure with access from the surface of the ground or from the sea.

Roget 221: interiority; inside, interior; interspace^†, subsoil, substratum; intrados.    contents etc. 190; substance, pith, marrow; backbone etc. (center) 222; heart, bosom, breast; abdomen; vitals, viscera, entrails, bowels, belly, intestines, guts, chitterings^†, womb, lap; penetralia [Lat.], recesses, innermost recesses; cave etc. (concavity) 252.    ... show more

Roget 189: abode, dwelling, lodging, domicile, residence, apartment, place, digs, pad, address, habitation, where one's lot is cast, local habitation, berth, diggings, seat, lap, sojourn, housing, quarters, headquarters, resiance^†, tabernacle, throne, ark.    home, fatherland; country; homestead, homestall^†; fireside; hearth, hearth stone; chimney corner, inglenook, ingle side; harem, seraglio, zenana^†; household gods, lares et penates [Lat.], roof, household, housing, dulce domum [Lat.], paternal domicile; native soil, native land.    habitat, range, stamping ground; haunt, hangout; biosphere; environment, ecological niche.    nest, nidus, snuggery^†; arbor, bower, etc. 191; lair, den, cave, hole, hiding place, cell, sanctum sanctorum [Lat.], aerie, eyrie, eyry^†, rookery, hive; covert, resort, retreat, perch, roost; nidification; kala jagah^†.    bivouac, camp, encampment, cantonment, castrametation^†; barrack, casemate^†, casern^†.    tent etc. (covering) 223; building etc. (construction) 161; chamber etc. (receptacle) 191; xenodochium^†.    tenement, messuage, farm, farmhouse, grange, hacienda, toft^†.    cot, cabin, hut, chalet, croft, shed, booth, stall, hovel, bothy^†, shanty, dugout [U.S.], wigwam; pen etc. (inclosure) 232; barn, bawn^†; kennel, sty, doghold^†, cote, coop, hutch, byre; cow house, cow shed; stable, dovecote, columbary^†, columbarium; shippen^†; igloo, iglu^†, jacal^†; lacustrine dwelling^†, lacuslake dwelling^†, lacuspile dwelling^†; log cabin, log house; shack, shebang [Slang], tepee, topek^†.    house, mansion, place, villa, cottage, box, lodge, hermitage, rus in urbe [Lat.], folly, rotunda, tower, chateau, castle, pavilion, hotel, court, manor-house, capital messuage, hall, palace; kiosk, bungalow; casa [Sp.], country seat, apartment house, flat house, frame house, shingle house, tenement house; temple etc. 1000.    hamlet, village, thorp^†, dorp^†, ham, kraal; borough, burgh, town, city, capital, metropolis; suburb; province, country; county town, county seat; courthouse [U.S.]; ghetto.    street, place, terrace, parade, esplanade, alameda^†, board walk, embankment, road, row, lane, alley, court, quadrangle, quad, wynd [Scot.], close [Scot.], yard, passage, rents, buildings, mews.    square, polygon, circus, crescent, mall, piazza, arcade, colonnade, peristyle, cloister; gardens, grove, residences; block of buildings, market place, place, plaza.    anchorage, roadstead, roads; dock, basin, wharf, quay, port, harbor.    quarter, parish etc. (region) 181.    assembly room, meetinghouse, pump room, spa, watering place; inn; hostel, hostelry; hotel, tavern, caravansary, dak bungalow^†, khan, hospice; public house, pub, pot house, mug house; gin mill, gin palace; bar, bar room; barrel house [U.S.], cabaret, chophouse; club, clubhouse; cookshop^†, dive [U.S.], exchange [Euph.]; grill room, saloon [U.S.], shebeen^†; coffee house, eating house; canteen, restaurant, buffet, cafe, estaminet^†, posada^†; almshouse^†, poorhouse, townhouse [U.S.].    garden, park, pleasure ground, plaisance^†, demesne.    [quarters for animals] cage, terrarium, doghouse; pen, aviary; barn, stall; zoo.    ... show more

Roget 191: receptacle; inclosure etc. 232; recipient, receiver, reservatory.    compartment; cell, cellule; follicle; hole, corner, niche, recess, nook; crypt, stall, pigeonhole, cove, oriel; cave etc. (concavity) 252.    capsule, vesicle, cyst, pod, calyx, cancelli, utricle, bladder; pericarp, udder.    stomach, paunch, venter, ventricle, crop, craw, maw, gizzard, breadbasket; mouth.    pocket, pouch, fob, sheath, scabbard, socket, bag, sac, sack, saccule, wallet, cardcase, scrip, poke, knit, knapsack, haversack, sachel, satchel, reticule, budget, net; ditty bag, ditty box; housewife, hussif; saddlebags; portfolio; quiver etc. (magazine) 636.    chest, box, coffer, caddy, case, casket, pyx, pix, caisson, desk, bureau, reliquary; trunk, portmanteau, band-box, valise; grip, grip sack [U.S.]; skippet, vasculum; boot, imperial; vache; cage, manger, rack.    vessel, vase, bushel, barrel; canister, jar; pottle, basket, pannier, buck-basket, hopper, maund^†, creel, cran, crate, cradle, bassinet, wisket, whisket, jardiniere, corbeille, hamper, dosser, dorser, tray, hod, scuttle, utensil; brazier; cuspidor, spittoon.    [For liquids] cistern etc. (store) 636; vat, caldron, barrel, cask, drum, puncheon, keg, rundlet, tun, butt, cag, firkin, kilderkin, carboy, amphora, bottle, jar, decanter, ewer, cruse, caraffe, crock, kit, canteen, flagon; demijohn; flask, flasket; stoup, noggin, vial, phial, cruet, caster; urn, epergne, salver, patella, tazza, patera; pig gin, big gin; tyg, nipperkin, pocket pistol; tub, bucket, pail, skeel, pot, tankard, jug, pitcher, mug, pipkin; galipot, gallipot; matrass, receiver, retort, alembic, bolthead, capsule, can, kettle; bowl, basin, jorum, punch bowl, cup, goblet, chalice, tumbler, glass, rummer, horn, saucepan, skillet, posnet^†, tureen.    [laboratory vessels for liquids] beaker, flask, Erlenmeyer flask, Florence flask, round-bottom flask, graduated cylinder, test tube, culture tube, pipette, Pasteur pipette, disposable pipette, syringe, vial, carboy, vacuum flask, Petri dish, microtiter tray, centrifuge tube.    bail, beaker, billy, canakin; catch basin, catch drain; chatti, lota, mussuk, schooner [U.S.], spider, terrine, toby, urceus.    plate, platter, dish, trencher, calabash, porringer, potager, saucer, pan, crucible; glassware, tableware; vitrics.    compote, gravy boat, creamer, sugar bowl, butter dish, mug, pitcher, punch bowl, chafing dish.    shovel, trowel, spoon, spatula, ladle, dipper, tablespoon, watch glass, thimble.    closet, commode, cupboard, cellaret, chiffonniere, locker, bin, bunker, buffet, press, clothespress, safe, sideboard, drawer, chest of drawers, chest on chest, highboy, lowboy, till, scrutoire^†, secretary, secretaire, davenport, bookcase, cabinet, canterbury; escritoire, etagere, vargueno, vitrine.    chamber, apartment, room, cabin; office, court, hall, atrium; suite of rooms, apartment [U.S.], flat, story; saloon, salon, parlor; by-room, cubicle; presence chamber; sitting room, best room, keeping room, drawing room, reception room, state room; gallery, cabinet, closet; pew, box; boudoir; adytum, sanctum; bedroom, dormitory; refectory, dining room, salle-a-manger; nursery, schoolroom; library, study; studio; billiard room, smoking room; den; stateroom, tablinum, tenement.    [room for defecation and urination] bath room, bathroom, toilet, lavatory, powder room; john, jakes, necessary, loo; [in public places] men's room, ladies' room, rest room; [fixtures] (uncleanness). 653 attic, loft, garret, cockloft, clerestory; cellar, vault, hold, cockpit; cubbyhole; cook house; entre-sol; mezzanine floor; ground floor, rez-de-chaussee; basement, kitchen, pantry, bawarchi-khana, scullery, offices; storeroom etc. (depository) 636; lumber room; dairy, laundry.    coach house; garage; hangar; outhouse; penthouse; lean-to.    portico, porch, stoop, stope, veranda, patio, lanai, terrace, deck; lobby, court, courtyard, hall, vestibule, corridor, passage, breezeway; ante room, ante chamber; lounge; piazza, veranda.    conservatory, greenhouse, bower, arbor, summerhouse, alcove, grotto, hermitage.    lodging etc. (abode) 189; bed etc. (support) 215; carriage etc. (vehicle) 272.    ... show more

Roget 252: concavity, depression, dip; hollow, hollowness; indentation, intaglio, cavity, dent, dint, dimple, follicle, pit, sinus, alveolus^†, lacuna; excavation, strip mine; trough etc. (furrow) 259; honeycomb.    cup, basin, crater, punch bowl; cell etc. (receptacle) 191; socket.    valley, vale, dale, dell, dingle, combe^†, bottom, slade^†, strath^†, glade, grove, glen, cave, cavern, cove; grot^†, grotto; alcove, cul-de-sac; gully etc. 198; arch etc. (curve) 245; bay etc. (of the sea) 343.    excavator, sapper, miner.    honeycomb (sponge) 252.1. ... show more

Dutch: hol, grot
Polish: jaskinia, pieczara, grota

Hollow out as if making a cave or opening.

synonym: undermine.

Dutch: ontwrichten

Explore natural caves.

synonym: spelunk.