The Collaborative International Dictionary of English v.0.48:

Constrictor \Con*strict"or\, n.
   1. That which constricts, draws together, or contracts.
      [1913 Webster]

   2. (Anat.) A muscle which contracts or closes an orifice, or
      which compresses an organ; a sphincter.
      [1913 Webster]

   3. (Zool.) A serpent that kills its prey by inclosing and
      crushing it with its folds; as, the boa constrictor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

constrictor
    n 1: any of various large nonvenomous snakes that kill their
         prey by crushing it in its coils