Hy"da*tid (?), n. [Gr. &?;, &?;, a watery vesicle under the upper eyelid, fr. "y`dwr, "y`datos, water: cf. F. hydatide.] (Zoöl.) A membranous sac or bladder filled with a pellucid fluid, found in various parts of the bodies of animals, but unconnected with the tissues. It is usually formed by parasitic worms, esp. by larval tapeworms, as Echinococcus and Cœnurus. See these words in the Vocabulary.

Hydatid of Morgagni(Anat.), one of the small pedunculated bodies found between the testicle and the head of the epididymis, and supposed to be a remnant of the Müllerian duct.