greasewood vs shrub

greasewood and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
greasewood	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of greasewood; that is, shrub is a word with a broader meaning than greasewood:

greasewood: low hardy much-branched spiny shrub common in alkaline soils of western America
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of greasewood include bush.

greasewood (noun)	shrub (noun)
low hardy much-branched spiny shrub common in alkaline soils of western America	a low woody perennial plant usually having several major stems