killjoy vs party pooper

killjoy and party pooper both are nouns.

Word	Noun	Adjective	Verb	Adverb
killjoy	Yes	No	No	No
party pooper	Yes	No	No	No

As nouns, killjoy and party pooper are synonyms defined as:

Other synonyms of killjoy include spoilsport, wet blanket.

killjoy (noun)	party pooper (noun)
someone who spoils the pleasure of others	someone who spoils the pleasure of others