unequal sides; scalene
Used in geometry to describe a triangle with three unequal sides (不等辺三角形). Also appears in other contexts where sides are of different lengths.
A scalene triangle is a triangle whose three sides are all different in length.
An equilateral triangle has all three sides equal, the opposite of 不等辺.
Compound of 不 (fu, 'not') + 等 (tō, 'equal') + 辺 (hen, 'side'), literally 'unequal sides'. A straightforward Sino-Japanese mathematical term.