civilian garb vs plain clothes

civilian garb and plain clothes both are nouns.

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

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

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

Other synonyms of civilian garb include civilian clothing, civilian dress.

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