THESAURUS
abysm, abyss, alveolation, alveolus, antrum, aperture, armpit, arroyo, basin, booth, bowl, box, box canyon, breach, break, broaching, canyon, cell, cellule, chamber, chap, chasm, check, chimney, chink, clearing, cleft, cleuch, clough, col, compartment, concave, concavity, coulee, couloir, crack, cranny, crater, crevasse, crevice, crib, crypt, cup, cut, cwm, deep, defile, dell, depression, depth, dike, dip, disclosure, ditch, donga, draw, enclosed space, excavation, fault, fenestra, fissure, fistula, flaw, flume, fold, follicle, fontanel, foramen, fracture, funnel chest, furrow, gap, gape, gash, gat, gorge, groove, gulch, gulf, gully, hiatus, hold, hole, hollow, hollow shell, incision, inlet, interval, joint, kloof, lacuna, laying open, leak, manger, moat, notch, nullah, opening, opening up, orifice, outlet, pass, passage, passageway, pew, pit, pocket, pore, punch bowl, ravine, rent, rift, rime, rupture, scissure, scoop, seam, shaft, shell, sink, sinus, slit, slot, socket, space, split, stall, stoma, throwing open, trench, trough, uncorking, unstopping, vacuity, valley, vault, void, vug, wadi, well, yawn, yawning abyss
ROGET THESAURUS
Concavity
N
concavity, depression, dip, hollow, hollowness, indentation, intaglio,
cavity, dent, dint, dimple, follicle, pit, sinus, alveolus, lacuna, excavation, strip mine, trough, honeycomb, cup, basin, crater, punch bowl, cell, socket, valley, vale, dale, dell, dingle, combe, bottom, slade, strath, glade, grove, glen, cave, cavern, cove, grot, grotto, alcove, cul-de- sac, gully, arch, bay, excavator, sapper, miner, honeycomb (sponge), depressed, alveolate, calathiform, cup-shaped, dishing, favaginous, faveolate, favose, scyphiform, scyphose, concave, hollow, stove in, retiring, retreating, cavernous, porous, infundibul, infundibular, infundibuliform, funnel shaped, bell shaped, campaniform, capsular, vaulted, arched.