The Collaborative International Dictionary of English v.0.48:

greasewood \greasewood\ n.
   A low hardy much-branched spiny shrub (Sarcobatus
   vermiculatus) common in alkaline soils of Western America.

   Syn: black greasewood, Sarcobatus vermiculatus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

greasewood
    n 1: low hardy much-branched spiny shrub common in alkaline
         soils of western America [syn: greasewood, black
         greasewood, Sarcobatus vermiculatus]