The Collaborative International Dictionary of English v.0.48:
Reentrant \Re*en"trant\ (-trant), a. Reentering; pointing or directed inwards; as, a reentrant angle. [1913 Webster]WordNet (r) 3.0 (2006):
reentrant adj 1: (of angles) pointing inward; "a polygon with re-entrant angles" [syn: re-entrant, reentrant] [ant: salient]