The Collaborative International Dictionary of English v.0.48:

Diorite \Di"o*rite\, n. [Cf. F. diorite. See Diorism.] (Min.)
   An igneous, crystalline in structure, consisting essentially
   of a triclinic feldspar and hornblende. It includes part of
   what was called greenstone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

diorite
    n 1: a granular crystalline intrusive rock