any freshwater or marine coelenterate of the class Hydrozoa, including free-swimming or attached types, as the hydra, in which
one developmental stage, either the polyp
or medusa, is absent, and colonial types, as the Portuguese man-of-war, in which both medusa and polyp stages are present in a single colony
belonging or pertaining to the Hydrozoa.
< Neo-Latin Hydrozo
) (see hydro-1
) + -an