The Collaborative International Dictionary of English v.0.48:

Contractility \Con`trac*til"i*ty\, n.
   1. The quality or property by which bodies shrink or
      contract.
      [1913 Webster]

   2. (Physiol.) The power possessed by the fibers of living
      muscle of contracting or shortening.
      [1913 Webster]

   Note: When subject to the will, as in the muscles of
         locomotion, such power is called voluntary
         contractility; when not controlled by the will, as in
         the muscles of the heart, it is involuntary
         contractility.
         [1913 Webster]

WordNet (r) 3.0 (2006):

contractility
    n 1: the capability or quality of shrinking or contracting,
         especially by muscle fibers and even some other forms of
         living matter