dead-man's float vs natation

dead-man's float and natation both are nouns.

Word	Noun	Adjective	Verb	Adverb
dead-man's float	Yes	No	No	No
natation	Yes	No	No	No

As nouns, natation is a hypernym of dead-man's float; that is, natation is a word with a broader meaning than dead-man's float:

dead-man's float: a floating position with the face down and arms stretched forward
natation: the act of someone who floats on the water

Other hypernyms of dead-man's float include floating.

dead-man's float (noun)	natation (noun)
a floating position with the face down and arms stretched forward	the act of someone who floats on the water