fir vs fir tree

fir and fir tree both are nouns.

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

As nouns, fir and fir tree are synonyms defined as:

fir and fir tree: any of various evergreen trees of the genus Abies; chiefly of upland areas

Other synonyms of fir include true fir.

fir (noun)	fir tree (noun)
any of various evergreen trees of the genus Abies; chiefly of upland areas	any of various evergreen trees of the genus Abies; chiefly of upland areas
nonresinous wood of a fir tree