celebration vs affair

celebration and affair both are nouns.

Word	Noun	Adjective	Verb	Adverb
celebration	Yes	No	No	No
affair	Yes	No	No	No

As nouns, affair is a hypernym of celebration; that is, affair is a word with a broader meaning than celebration:

celebration: a joyful occasion for special festivities to mark some happy event
affair: a formal or official social gathering or ceremony of people

Other hypernyms of celebration include function, occasion, social affair, social function, social gathering, social occasion.

celebration (noun)	affair (noun)
any joyous diversion	a vaguely specified concern
the public performance of a sacrament or solemn ceremony with all appropriate ritual	a formal or official social gathering or ceremony of people
a joyful occasion for special festivities to mark some happy event	a usually secretive or illicit sexual relationship