swimming vs skin diving

swimming and skin diving both are nouns.

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

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

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

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

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

swimming (adjective)	skin diving (adjective)
applied to a fish depicted horizontally
filled or brimming with tears