swan vs black swan

swan and black swan both are nouns.

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

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

swan: stately heavy-bodied aquatic bird with very long neck and usually white plumage as adult
black swan: large Australian swan having black plumage and a red bill

swan (noun)	black swan (noun)
stately heavy-bodied aquatic bird with very long neck and usually white plumage as adult	large Australian swan having black plumage and a red bill

swan (verb)	black swan (verb)
to declare or affirm solemnly and formally as true
move about aimlessly or without any destination, often in search of food or employment
sweep majestically