Zool. [a. mod.L. Unionid-æ (see def.), f. L. unio UNIO: see -ID3.] A member of the Unionidæ, a large family of bivalve mollusks typified by the genus Unio of freshwater mussels; a unio.
1861. P. P. Carpenter, in Rep. Smithsonian Instit. 1860, 263. The extreme forms of the Unionids.
