sleepover vs affair

sleepover and affair both are nouns.

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

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

sleepover: an occasion of spending a night away from home or having a guest spend the night in your home (especially as a party for children)
affair: a formal or official social gathering or ceremony of people

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

sleepover (noun)	affair (noun)
an occasion of spending a night away from home or having a guest spend the night in your home (especially as a party for children)	a vaguely specified concern
	a formal or official social gathering or ceremony of people
	a usually secretive or illicit sexual relationship