The Collaborative International Dictionary of English v.0.48:

Cavity \Cav"i*ty\, n.; pl. Cavities. [L. cavus hollow: cf. F.
   cavit['e].]
   1. Hollowness. [Obs.]
      [1913 Webster]

            The cavity or hollowness of the place. --Goodwin.
      [1913 Webster]

   2. A hollow place; a hollow; as, the abdominal cavity.
      [1913 Webster]

            An instrument with a small cavity, like a small
            spoon.                                --Arbuthnot.
      [1913 Webster]

            Abnormal spaces or excavations are frequently formed
            in the lungs, which are designated cavities or
            vomic[ae].                            --Quain.
      [1913 Webster]

   Body cavity, the c[oe]lum. See under Body.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cavity
    n 1: a sizeable hole (usually in the ground); "they dug a pit to
         bury the body" [syn: pit, cavity]
    2: space that is surrounded by something [syn: cavity,
       enclosed space]
    3: soft decayed area in a tooth; progressive decay can lead to
       the death of a tooth [syn: cavity, caries, dental
       caries, tooth decay]
    4: (anatomy) a natural hollow or sinus within the body [syn:
       cavity, bodily cavity, cavum]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "cavity":
   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