gray sage vs sagebrush

gray sage and sagebrush both are nouns.

Word	Noun	Adjective	Verb	Adverb
gray sage	Yes	No	No	No
sagebrush	Yes	No	No	No

As nouns, sagebrush is a hypernym of gray sage; that is, sagebrush is a word with a broader meaning than gray sage:

gray sage: low much-branched perennial of western United States having silvery leaves; an important browse and shelter plant
sagebrush: any of several North American composite subshrubs of the genera Artemis or Seriphidium

Other hypernyms of gray sage include sage brush.

gray sage (noun)	sagebrush (noun)
low much-branched perennial of western United States having silvery leaves; an important browse and shelter plant	any of several North American composite subshrubs of the genera Artemis or Seriphidium