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):

squill
    n 1: bulb of the sea squill, which is sliced, dried, and used as
         an expectorant
    2: having dense spikes of small white flowers and yielding a
       bulb with medicinal properties [syn: sea squill, sea
       onion, squill, Urginea maritima]
    3: an Old World plant of the genus Scilla having narrow basal
       leaves and pink or blue or white racemose flowers [syn:
       scilla, squill]