dewberry vs blackberry bush

dewberry and blackberry bush both are nouns.

Word	Noun	Adjective	Verb	Adverb
dewberry	Yes	No	No	No
blackberry bush	Yes	No	No	No

As nouns, blackberry bush is a hypernym of dewberry; that is, blackberry bush is a word with a broader meaning than dewberry:

dewberry: any of several trailing blackberry brambles especially of North America
blackberry bush: bramble with sweet edible black or dark purple berries that usually do not separate from the receptacle

Other hypernyms of dewberry include blackberry.

dewberry (noun)	blackberry bush (noun)
blackberry-like fruits of any of several trailing blackberry bushes	bramble with sweet edible black or dark purple berries that usually do not separate from the receptacle
any of several trailing blackberry brambles especially of North America