The Collaborative International Dictionary of English v.0.48:
Pentangular \Pen*tan"gu*lar\, a. [Penta- + angular.] Having five corners or angles. [R.] [1913 Webster]WordNet (r) 3.0 (2006):
pentangular adj 1: of or relating to or shaped like a pentagon [syn: pentangular, pentagonal]