lowland white fir vs silver fir

lowland white fir and silver fir both are nouns.

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

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

lowland white fir: lofty fir of the Pacific coast of northwestern America having long curving branches and deep green leaves
silver fir: any of various true firs having leaves white or silvery white beneath

lowland white fir (noun)	silver fir (noun)
lofty fir of the Pacific coast of northwestern America having long curving branches and deep green leaves	any of various true firs having leaves white or silvery white beneath