forties vs decade

forties and decade both are nouns.

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

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

Other hypernyms of forties include decennary, decennium.

forties (noun)	decade (noun)
the time of life between 40 and 50	the cardinal number that is the sum of nine and one; the base of the decimal system
the decade from 1940 to 1949	a period of 10 years