Source : Webster's Revised Unabridged Dictionary (1913)

Evolute \Ev"o*lute\, n. [L. evolutus unrolled, p. p. of
   evolvere. See {Evolve}.] (Geom.)
   A curve from which another curve, called the involute or
   evolvent, is described by the end of a thread gradually wound
   upon the former, or unwound from it. See {Involute}. It is
   the locus of the centers of all the circles which are
   osculatory to the given curve or evolvent.

   Note: Any curve may be an evolute, the term being applied to
         it only in its relation to the involute.