true fir vs coniferous tree

true fir and coniferous tree both are nouns.

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

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

true fir: any of various evergreen trees of the genus Abies; chiefly of upland areas
coniferous tree: any gymnospermous tree or shrub bearing cones

Other hypernyms of true fir include conifer.

true fir (noun)	coniferous tree (noun)
any of various evergreen trees of the genus Abies; chiefly of upland areas	any gymnospermous tree or shrub bearing cones