The Collaborative International Dictionary of English v.0.48:

Zooid \Zo"oid\, a. [Zoo- + -oid.] (Biol.)
   Pertaining to, or resembling, an animal.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Zooid \Zo"oid\, n.
   1. (Biol.) An organic body or cell having locomotion, as a
      spermatic cell or spermatozooid.
      [1913 Webster]

   2. (Zool.)
      (a) An animal in one of its inferior stages of
          development, as one of the intermediate forms in
          alternate generation.
      (b) One of the individual animals in a composite group, as
          of Anthozoa, Hydroidea, and Bryozoa; -- sometimes
          restricted to those individuals in which the mouth and
          digestive organs are not developed.
          [1913 Webster]

WordNet (r) 3.0 (2006):

zooid
    n 1: one of the distinct individuals forming a colonial animal
         such as a bryozoan or hydrozoan