swim vs backstroke

swim and backstroke both are nouns.

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

As verbs, backstroke is a hyponym of swim; that is, backstroke is a word with a more specific, narrower meaning than swim:

Other hyponyms of swim include bathe, school, break water, fin, fin, paddle, crawl, breaststroke, dive.

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

swim (verb)	backstroke (verb)
travel through water	swim on one's back
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