full gainer vs diving

full gainer and diving both are nouns.

Word	Noun	Adjective	Verb	Adverb
full gainer	Yes	No	No	No
diving	Yes	No	No	No

As nouns, diving is a hypernym of full gainer; that is, diving is a word with a broader meaning than full gainer:

full gainer: a dive in which the diver throws the feet forward to complete a full backward somersault and enters the water feet first and facing away from the diving board
diving: a headlong plunge into water

Other hypernyms of full gainer include dive.

full gainer (noun)	diving (noun)
a dive in which the diver throws the feet forward to complete a full backward somersault and enters the water feet first and facing away from the diving board	a headlong plunge into water
	an athletic competition that involves diving into water