swim vs skin diving

swim and skin diving both are nouns.

Word	Noun	Adjective	Verb	Adverb
swim	Yes	No	Yes	No
skin diving	Yes	No	No	No

As nouns, skin diving is a hyponym of swim; that is, skin diving is a word with a more specific, narrower meaning than swim:

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

Other hyponyms of swim include bathe, skinny-dip, dip, plunge, dive, diving, floating, natation, skin-dive.

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

swim (verb)	skin diving (verb)
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