aquanaut vs bather

aquanaut and bather both are nouns.

Word	Noun	Adjective	Verb	Adverb
aquanaut	Yes	No	No	No
bather	Yes	No	No	No

As nouns, bather is a hypernym of aquanaut; that is, bather is a word with a broader meaning than aquanaut:

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

Other hypernyms of aquanaut include natator, swimmer.

aquanaut (noun)	bather (noun)
an underwater swimmer equipped with a face mask and foot fins and either a snorkel or an air cylinder	a person who travels through the water by swimming
a skilled worker who can live in underwater installations and participate in scientific research	a person who takes a bath