del·toid / ˈdeltoid/ • adj. technical triangular: a tree with large deltoid leaves. ∎  denoting a thick triangular muscle covering the shoulder joint and used for raising the arm away from the body.• n. a deltoid muscle. ∎  each of the three parts of a deltoid muscle, attached at the front, side, and rear of the shoulder: the anterior deltoid.

deltoid (del-toid) n. a thick triangular muscle that covers the shoulder joint. It is responsible for raising the arm from the side of the body.