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c.1400, from Old French concavité "hollow, concavity" (14c.) or directly from Latin concavitatem (nominative concavitas), from Latin concavus "hollow" (see concave).
concavity con·cav·i·ty (kŏn-kāv'ĭ-tē)n. A hollow or depression that is curved like the inner surface of a sphere.