bather vs skin-diver

bather and skin-diver both are nouns.

Word	Noun	Adjective	Verb	Adverb
bather	Yes	No	No	No
skin-diver	Yes	No	No	No

As nouns, skin-diver is a hyponym of bather; that is, skin-diver is a word with a more specific, narrower meaning than bather:

bather: a person who travels through the water by swimming
skin-diver: an underwater swimmer equipped with a face mask and foot fins and either a snorkel or an air cylinder

Other hyponyms of bather include floater, aquanaut, surfboarder, surfer.

bather (noun)	skin-diver (noun)
a person who travels through the water by swimming	an underwater swimmer equipped with a face mask and foot fins and either a snorkel or an air cylinder
a person who takes a bath