The Collaborative International Dictionary of English v.0.48:
Isosceles \I*sos"ce*les\, a. [L., fr. Gr. ?; 'i`sos equal + ? leg.] (Geom.) Having two legs or sides that are equal; -- said of a triangle. [1913 Webster]WordNet (r) 3.0 (2006):
isosceles adj 1: (of a triangle) having two sides of equal length