2. (Science: botany) Oblong or elongated, and having three lateral angles; as, a triangular seed, leaf, or stem. Triangular compasses, compasses with three legs for taking off the angular points of a triangle, or any three points at the same time.
(Science: mathematics) Triangular numbers, the series of numbers formed by the successive sums of the terms of an arithmetical progression, of which the first term and the common difference are 1. See figurate numbers, under Figurate.
Origin: L. Triangularis: cf. F. Triangulaire.