triceps, n. [NL., fr. L. triceps, having three beads; tres, tria, three + caput head: cf. F. triceps. See Three, and Chief.].
A muscle having three heads; specif., the great extensor of the forearm, arising by three heads and inserted into the olecranon at the elbow. [1913 Webster]
triceps, adj. & n.
--adj. (of a muscle) having three heads or points of attachment.
--n. any triceps muscle, esp. the large muscle at the back of the upper arm.