silver fir vs fir

silver fir and fir both are nouns.

Word	Noun	Adjective	Verb	Adverb
silver fir	Yes	No	No	No
fir	Yes	No	No	No

As nouns, fir is a hypernym of silver fir; that is, fir is a word with a broader meaning than silver fir:

silver fir: any of various true firs having leaves white or silvery white beneath
fir: any of various evergreen trees of the genus Abies; chiefly of upland areas

Other hypernyms of silver fir include fir tree, true fir.

silver fir (noun)	fir (noun)
any of various true firs having leaves white or silvery white beneath	any of various evergreen trees of the genus Abies; chiefly of upland areas
	nonresinous wood of a fir tree