special-interest group vs lobby group

special-interest group and lobby group both are nouns.

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

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

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

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

special-interest group (noun)	lobby 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