Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

deltoid
     adj : of a leaf shape; suggesting a capital delta, with a point at
           the apex

deltoid
     n : a large triangular muscle covering the shoulder joint and
         serving to abduct and flex and extend and rotate the arm
         [syn: {deltoid muscle}, {musculus deltoideus}]