Source : Webster's Revised Unabridged Dictionary (1913)

Reenter \Re*["e]n"ter\, v. i.
   To enter anew or again.

   {Re["e]ntering angle}, an angle of a polygon pointing inward,
      as a, in the cut.

   {Re["e]ntering polygon}, a polygon having one or more
      re["e]ntering angles.

Source : WordNet®

reentering angle
     n : an interior angle of a polygon that is greater than 180
         degrees [syn: {reentrant angle}] [ant: {salient angle}]