Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. [pl. {Medusae}.] (Zo["o]l.) Any free swimming acaleph; a
      jellyfish.

   Note: The larger medus[ae] belong to the Discophora, and are
         sometimes called {covered-eyed medus[ae]}; others,
         known as {naked-eyed medus[ae]}, belong to the
         Hydroidea, and are usually developed by budding from
         hidroids. See {Discophora}, {Hydroidea}, and
         {Hydromedusa}.

   {Medusa bud} (Zo["o]l.), one of the buds of a hydroid,
      destined to develop into a gonophore or medusa. See
      {Athecata}, and {Gonotheca}.

   {Medusa's head}.
      (a) (Zo["o]l.) An astrophyton.
      (b) (Astron.) A cluster of stars in the constellation
          Perseus. It contains the bright star Algol.

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

   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}.