The Collaborative International Dictionary of English v.0.48:

Squill \Squill\ (skw[i^]l), n. [F. squille (also scille a
   squill, in sense 1), L. squilla, scilla, Gr. ?.]
   1. (Bot.)
      (a) A European bulbous liliaceous plant (Urginea
          maritima, formerly Scilla maritima), of acrid,
          expectorant, diuretic, and emetic properties, used in
          medicine. Called also sea onion.
      (b) Any bulbous plant of the genus Scilla; as, the
          bluebell squill (Scilla mutans).
          [1913 Webster]

   2. (Zool.)
      (a) A squilla.
      (b) A mantis.
          [1913 Webster]

WordNet (r) 3.0 (2006):

Urginea maritima
    n 1: having dense spikes of small white flowers and yielding a
         bulb with medicinal properties [syn: sea squill, sea
         onion, squill, Urginea maritima]