firethorn vs shrub

firethorn and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
firethorn	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of firethorn; that is, shrub is a word with a broader meaning than firethorn:

firethorn: any of various thorny shrubs of the genus Pyracantha bearing small white flowers followed by hard red or orange-red berries
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of firethorn include bush.

firethorn (noun)	shrub (noun)
any of various thorny shrubs of the genus Pyracantha bearing small white flowers followed by hard red or orange-red berries	a low woody perennial plant usually having several major stems