sheep vs black sheep

sheep and black sheep both are nouns.

Word	Noun	Adjective	Verb	Adverb
sheep	Yes	No	No	No
black sheep	Yes	No	No	No

As nouns, black sheep is a hyponym of sheep; that is, black sheep is a word with a more specific, narrower meaning than sheep:

Other hyponyms of sheep include ewe, ram, tup, wether, domestic sheep, Ovis aries.

sheep (noun)	black sheep (noun)
woolly usually horned ruminant mammal related to the goat	sheep with a black coat
a docile and vulnerable person who would rather follow than make an independent decision	a reckless and unprincipled reprobate
a timid defenseless simpleton who is readily preyed upon