Del″toid (?), a. [Gr. δελτοειδήσ delta- shaped; δέλτα the name of the letter Δ + εἰ̑δοσ form: cf. F. deltoïde. See Delta.] Shaped like the Greek Δ (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.