(Of a triangle) having two equal sides (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
isosceles
(Other definitions for isosceles that I've seen before include "Describing a triangle with two equal sides" , "(Of triangles) having two sides the same" , "Kind of triangle" , "Triangle with two sides of equal length" , "Of triangular, with two sides of equal length" .)