butcher's broom vs shrub

butcher's broom and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
butcher's broom	Yes	No	No	No
shrub	Yes	No	No	No

As nouns, shrub is a hypernym of butcher's broom; that is, shrub is a word with a broader meaning than butcher's broom:

butcher's broom: shrub with stiff flattened stems resembling leaves (cladophylls); used for making brooms
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of butcher's broom include bush.

butcher's broom (noun)	shrub (noun)
shrub with stiff flattened stems resembling leaves (cladophylls); used for making brooms	a low woody perennial plant usually having several major stems