Webster’s Revised Unabridged Dictionary · 1913 Polybranchia Pol′y·bran′chi·a (pŏl′ĭ·brăn̲′kĭ·ȧ), n. pl. [NL. See Poly-, and Branchia.] (Zoöl.) A division of Nudibranchiata including those which have numerous branchiæ on the back. ‹ Polybasite Polybromide ›