cotton plant vs shrub

cotton plant and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton plant	Yes	No	No	No
shrub	Yes	No	No	No

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

cotton plant: erect bushy mallow plant or small tree bearing bolls containing seeds with many long hairy fibers
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of cotton plant include bush.

cotton plant (noun)	shrub (noun)
erect bushy mallow plant or small tree bearing bolls containing seeds with many long hairy fibers	a low woody perennial plant usually having several major stems