retirement fund vs old-age pension

retirement fund and old-age pension both are nouns.

Word	Noun	Adjective	Verb	Adverb
retirement fund	Yes	No	No	No
old-age pension	Yes	No	No	No

As nouns, retirement fund and old-age pension are synonyms defined as:

retirement fund and old-age pension: a monthly payment made to someone who is retired from work

Other synonyms of retirement fund include retirement benefit, retirement check, retirement pension, superannuation.

retirement fund (noun)	old-age pension (noun)
a monthly payment made to someone who is retired from work	a monthly payment made to someone who is retired from work