pressure group vs special interest group

pressure group and special interest group both are nouns.

Word	Noun	Adjective	Verb	Adverb
pressure group	Yes	No	No	No
special interest group	Yes	No	No	No

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

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

pressure 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