seatbelt vs life belt

seatbelt and life belt both are nouns.

Word	Noun	Adjective	Verb	Adverb
seatbelt	Yes	No	No	No
life belt	Yes	No	No	No

As nouns, life belt is a hypernym of seatbelt; that is, life belt is a word with a broader meaning than seatbelt:

seatbelt: a safety belt used in a car or plane to hold you in your seat in case of an accident
life belt: belt attaching you to some object as a restraint in order to prevent you from getting hurt

Other hypernyms of seatbelt include safety belt, safety harness.

seatbelt (noun)	life belt (noun)
a safety belt used in a car or plane to hold you in your seat in case of an accident	a life preserver in the form of a ring of buoyant material
	belt attaching you to some object as a restraint in order to prevent you from getting hurt