Source : Webster's Revised Unabridged Dictionary (1913)

Pleonaste \Ple"o*naste\, n. [Gr.? abundant, rich; cf. F.
   pl['e]onaste.] (Min.)
   A black variety of spinel.

Source : WordNet®

pleonaste
     n : a dark-colored spinel containing iron [syn: {Ceylonite}]