Deltoid \Del"toid\, a. [Gr. deltoeidh`s delta- shaped; de`lta the name of the letter [Delta] + e'i^dos form: cf. F. delto["i]de. See Delta.]

Shaped like the Greek [Delta] (delta); delta-shaped; triangular.

Deltoid leaf (Bot.), a leaf in the form of a triangle with the stem inserted at the middle of the base.

Deltoid muscle (Anat.), a triangular muscle in the shoulder which serves to move the arm directly upward.

Source: Webster's Revised Unabridged Dictionary (1913)