skin-dive vs swim

skin-dive and swim both are nouns.

Word	Noun	Adjective	Verb	Adverb
skin-dive	Yes	No	Yes	No
swim	Yes	No	Yes	No

As nouns, swim is a hypernym of skin-dive; that is, swim is a word with a broader meaning than skin-dive:

skin-dive: underwater swimming without any more breathing equipment than a snorkel
swim: the act of swimming

Other hypernyms of skin-dive include swimming.

skin-dive (noun)	swim (noun)
underwater swimming without any more breathing equipment than a snorkel	the act of swimming

skin-dive (verb)	swim (verb)
swim underwater with no breathing apparatus other than a snorkel	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