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.

Source : WordNet®

Medusa
     n 1: (Greek mythology) a woman transformed into a Gorgon by
          Athena; she was slain by Perseus
     2: any of numerous usually marine and free-swimming
        coelenterates that constitute the sexually reproductive
        forms of hydrozoans and scyphozoans [syn: {jellyfish}, {medusan}]
     3: one of two forms that coelenterates take: is the
        free-swimming sexual stage in the life cycle of a
        coelenterate and has a gelatinous umbrella-shaped body and
        tentacles