isosceles

from WordNet (r) 3.0 (2006)

isosceles
    adj 1: (of a triangle) having two sides of equal length

from 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]