advocacy group vs special-interest group

advocacy group and special-interest group both are nouns.

Word	Noun	Adjective	Verb	Adverb
advocacy group	Yes	No	No	No
special-interest group	Yes	No	No	No

As nouns, advocacy group and special-interest group are synonyms defined as:

advocacy group and special-interest group: an interest group that tries to influence legislators or bureaucrats to act in their favor, typically through lobbying

Other synonyms of advocacy group include lobby, lobby group, pressure group, special interest, special interest group, third house.

advocacy group (noun)	special-interest group (noun)
an interest group that tries to influence legislators or bureaucrats to act in their favor, typically through lobbying	an interest group that tries to influence legislators or bureaucrats to act in their favor, typically through lobbying