Source : Webster's Revised Unabridged Dictionary (1913)

Anorthosite \A*nor"tho*site\, n. [F. anorthose triclinic
   feldspar (fr. Gr. ? priv. + ? straight) + -ite.] (Petrol.)
   A granular igneous rock composed almost exclusively of a
   soda-lime feldspar, usually labradorite.