plain clothes vs civilian garb

plain clothes and civilian garb both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain clothes	Yes	No	No	No
civilian garb	Yes	No	No	No

As nouns, plain clothes and civilian garb are synonyms defined as:

plain clothes and civilian garb: ordinary clothing as distinguished from uniforms, work clothes, clerical garb, etc.

Other synonyms of plain clothes include civilian clothing, civilian dress.

plain clothes (noun)	civilian garb (noun)
ordinary clothing as distinguished from uniforms, work clothes, clerical garb, etc.	ordinary clothing as distinguished from uniforms, work clothes, clerical garb, etc.