'Hydroid' definitions:

Definition of 'hydroid'

(from WordNet)
noun
Colonial coelenterates having the polyp phase dominant [syn: hydrozoan, hydroid]

Definition of 'Hydroid'

From: GCIDE
  • Hydroid \Hy"droid\, a. [Hydra + -oid.] (Zool.) Related to, or resembling, the hydra; of or pertaining to the Hydroidea. -- n. One of the Hydroideas. [1913 Webster]