Source : Webster's Revised Unabridged Dictionary (1913)

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

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

   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.

Source : WordNet®

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