working group vs working party

working group and working party both are nouns.

Word	Noun	Adjective	Verb	Adverb
working group	Yes	No	No	No
working party	Yes	No	No	No

As nouns, working group and working party are synonyms defined as:

working group and working party: a group of people working together temporarily until some goal is achieved

working group (noun)	working party (noun)
a group of people working together temporarily until some goal is achieved	a group of people working together temporarily until some goal is achieved