n. pl. an·tra(ăntrə)
1. A cavity or chamber, especially one in a bone.
2. Either of the sinuses in the bones of the upper jaw, opening into the nasal cavity.
[Late Latin, cavity in the body, from Latin, cave, from Greek antron, back-formed singular from plural antra, possibly originally a collective of earlier *antēr, cave, of unknown origin; possibly akin to Armenian ayr, cave, also from earlier *antēr.]
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