backstroke vs swim

backstroke and swim both are nouns.

Word	Noun	Adjective	Verb	Adverb
backstroke	Yes	No	Yes	No
swim	Yes	No	Yes	No

As verbs, swim is a hypernym of backstroke; that is, swim is a word with a broader meaning than backstroke:

backstroke (noun)	swim (noun)
a swimming stroke that resembles the crawl except the swimmer lies on his or her back	the act of swimming

backstroke (verb)	swim (verb)
swim on one's back	travel through water
	be afloat either on or below a liquid surface and not sink to the bottom
	move as if gliding through water
	be covered with or submerged in a liquid
	be dizzy or giddy