Like triangles with unequal sides (7)
I believe the answer is:
scalene
'like triangles with unequal sides' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scalene that I've seen before include "Neither equilateral nor isosceles" , "not having evenly matched sides" , "(Of triangle) with each side of a different length" , "Describing a triangle with unequal sides" , "(Of triangle) having three unequal sides" .)