The word "triceps" is a direct borrowing from Latin, where it functioned as an adjective meaning "three-headed". It is formed from the combination of 'tri-' (three) and '-ceps', a variant of 'caput' (head). In anatomical Latin, it was used in phrases like 'musculus triceps brachii', literally "the three-headed muscle of the arm", describing the muscle's structure which originates from three distinct points on the shoulder blade and upper arm bone. This literal, descriptive term was adopted into English in the 16th century, retaining its precise anatomical reference to the muscle's multi-headed form.

Structure: tri (three) + ceps (head) - tri: From Latin, meaning "three". A numerical prefix. - ceps: From Latin 'caput', meaning "head". In anatomical terms, it refers to the heads or points of origin of a muscle.