red osier vs dogwood

red osier and dogwood both are nouns.

Word	Noun	Adjective	Verb	Adverb
red osier	Yes	No	No	No
dogwood	Yes	No	No	No

As nouns, dogwood is a hypernym of red osier; that is, dogwood is a word with a broader meaning than red osier:

red osier: common North American shrub with reddish purple twigs and white flowers
dogwood: a tree of shrub of the genus Cornus often having showy bracts resembling flowers

Other hypernyms of red osier include cornel, dogwood tree.

red osier (noun)	dogwood (noun)
Eurasian osier having reddish or purple twigs and bark rich in tannin	a tree of shrub of the genus Cornus often having showy bracts resembling flowers
common North American shrub with reddish purple twigs and white flowers	hard tough wood of any dogwood of the genus Cornus; resembles boxwood