fifties vs decade

fifties and decade both are nouns.

Word	Noun	Adjective	Verb	Adverb
fifties	Yes	No	No	No
decade	Yes	No	No	No

As nouns, decade is a hypernym of fifties; that is, decade is a word with a broader meaning than fifties:

Other hypernyms of fifties include decennary, decennium.

fifties (noun)	decade (noun)
the time of life between 50 and 60	the cardinal number that is the sum of nine and one; the base of the decimal system
the decade from 1950 to 1959	a period of 10 years