equilateral

the word equilateral is a modern latin formation, entering english in the 16th century from the late latin "aequilaterus." it is a compound of two classical latin roots: "aequi-" (equal) and "latus" (side). the root "aequi-" derives from the proto-indo-european h₁éḱwos, meaning "horse" and by extension "equal," as horses were often exchanged as measures of value. "latus" is of uncertain origin but has been used in latin specifically to denote the side of a geometric figure. the suffix "-al" is a common adjectival ending. thus, the term's literal meaning, "having equal sides," is a direct and logical description of its geometric application, perfectly preserving the original semantic intent of its constituent parts.