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 leaf
     n : shaped like a capital delta