The Collaborative International Dictionary of English v.0.48:

Hydromedusa \Hy`dro*me*du"sa\, n.; pl. Hydromedus[ae]. [NL.
   See Hydra, and Medusa.] (Zool.)
   Any medusa or jellyfish which is produced by budding from a
   hydroid. They are called also Craspedota, and naked-eyed
   medus[ae].
   [1913 Webster]

   Note: Such medus[ae] are the reproductive zooids or
         gonophores, either male or female, of the hydroid from
         which they arise, whether they become free or remain
         attached to the hydroid colony. They in turn produce
         the eggs from which the hydroids are developed. The
         name is also applied to other similar medus[ae] which
         are not known to bud from a hydroid colony, and even to
         some which are known to develop directly from the eggs,
         but which in structure agree essentially with those
         produced from hydroids. See Hydroidea, and
         Gymnoblastea.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Medusa \Me*du"sa\, n. [L., fr. Gr. ?.]
   1. (Class. Myth.) The Gorgon; or one of the Gorgons whose
      hair was changed into serpents, after which all who looked
      upon her were turned into stone.
      [1913 Webster]

   2. [pl. Medusae.] (Zool.) Any free swimming acaleph; a
      jellyfish.
      [1913 Webster]

   Note: The larger medusae belong to the Discophora, and are
         sometimes called covered-eyed medusae; others, known
         as naked-eyed medusae, belong to the Hydroidea, and
         are usually developed by budding from hydroids. See
         Discophora, Hydroidea, and Hydromedusa.
         [1913 Webster]

   Medusa bud (Zool.), one of the buds of a hydroid, destined
      to develop into a gonophore or medusa. See Athecata, and
      Gonotheca.

   Medusa's head.
      (a) (Zool.) An astrophyton.
      (b) (Astron.) A cluster of stars in the constellation
          Perseus. It contains the bright star Algol.
          [1913 Webster]