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.]
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            The cavity or hollowness of the place. --Goodwin.
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   2. A hollow place; a hollow; as, the abdominal cavity.
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            An instrument with a small cavity, like a small
            spoon.                                --Arbuthnot.
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            Abnormal spaces or excavations are frequently formed
            in the lungs, which are designated cavities or
            vomic[ae].                            --Quain.
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   Body cavity, the c[oe]lum. See under Body.
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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]