Hŷd'a-tĭd, n.

(Synop., § 130), n. [Fr. hydatide, Gr. ὑδατίς, -ίδος, a watery vesicle under the upper eyelid, from ὕδωρ, ὕδατος, water.] (Zool.) A membranous sac or bladder filled with a pellucid fluid, found parasitic in various parts of the body of organized beings, but unconnected with the tissues. It is often formed by parasitic animals.