big sagebrush vs blue sage

big sagebrush and blue sage both are nouns.

Word	Noun	Adjective	Verb	Adverb
big sagebrush	Yes	No	No	No
blue sage	Yes	No	No	No

As nouns, big sagebrush and blue sage are synonyms defined as:

big sagebrush and blue sage: aromatic shrub of arid regions of western North America having hoary leaves

Other synonyms of big sagebrush include Artemisia tridentata, Seriphidium tridentatum.

big sagebrush (noun)	blue sage (noun)
aromatic shrub of arid regions of western North America having hoary leaves	aromatic shrub of arid regions of western North America having hoary leaves
	blue-flowered sage of dry prairies of the eastern United States
	Texas sage having intensely blue flowers
	sage of western North America to Central America having violet-blue flowers; widespread in cultivation