swan vs cob

swan and cob both are nouns.

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

As nouns, cob is a hyponym of swan; that is, cob 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
cob: adult male swan

swan (noun)	cob (noun)
stately heavy-bodied aquatic bird with very long neck and usually white plumage as adult	adult male swan
	stocky short-legged harness horse
	white gull having a black back and wings
	nut of any of several trees of the genus Corylus

swan (verb)	cob (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