Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class II. Words Relating to Space
Section III. Form
3. Superficial Form

252. Concavity.

   NOUN:CONCAVITY, depression, dip; hollow, hollowness; indentation, intaglio, cavity, vug or vugg or vugh, dent, dint, dimple, follicle, pit, sinus, antrum, alveolus, lacuna; honeycomb.
  EXCAVATION, pit, sap, mine, shaft, colliery; caisson, fougasse [F.], countermine; trough (furrow) [See Furrow]; bay &c. (of the sea) [See Gulf; Lake].
  cup, basin, crater, punch bowl; cell (receptacle) [See Receptacle]; socket.
  VALLEY, vale, dale, dell, dingle, coomb or combe, bottom, slade [obs.], strath [Scot.], gill or ghyll [Scot. & dial. Eng.], glade, grove, glen, donga [S. Africa], nullah [India], park [U. S.].
  CAVE, subterrane, cavern, cove; grot, grotto; alcove, blind alley, cul-de-sac [F.], hole, burrow, kennel, tunnel; gully [See Interval]; arch (curve) [See Curvature].
  EXCAVATOR, sapper, miner.
   VERB:BE CONCAVE &c. adj.; retire, cave in.
  RENDER CONCAVE &c. adj.; depress, dish, hollow; scoop, scoop out; gouge, dig, delve, excavate, dent, dint, mine, sap, undermine, burrow, tunnel, stave in.
   ADJECTIVE:DEPRESSED &c. v.; alveolate, alveolar, calathiform, cup-shaped, dishing; favaginous, faveolate, favose; scyphiform, scyphose; concave, hollow, vuggy, stove in; retiring; retreating; cavernous; porous &c. (with holes) [See Opening]; cellular, spongy, spongious; honeycombed; infundibular, infundibuliform, funnel-shaped, bell-shaped, campaniform, capsular; vaulted, arched.