Entry 1 sense Webster, 1913 Isosceles /īs-ôs'-əl-ēzˌ/ · I·sos·ce·les · IPA /aɪˈsɑsəliz/ 01 a. Having two legs or sides that are equal; -- said of a triangle. 1. Having two legs or sides that are equal; -- said of a triangle.(Geom.)