spoilsport vs party pooper

spoilsport and party pooper both are nouns.

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

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

Other synonyms of spoilsport include killjoy, wet blanket.

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