hydatid (hy-dă-tid) n. a bladder-like cyst formed in various human tissues following the growth of the larval stage of an Echinococcus tapeworm. alveolar h. an aggregate of small cysts, which enlarge by budding off external daughter cysts. unilocular h. a single large fluid-filled cyst, bound by a fibrous capsule, that gives rise internally to smaller daughter cysts. See also hydatid disease.

hydatid (path.)watery cyst. XVII (in L. pl. form hydatides). — modL. hydatis, -id- — Gr. hudatis, -id-, f. hūdōr, hudat- WATER; see -ID2.