plain clothes vs mufti

plain clothes and mufti both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain clothes	Yes	No	No	No
mufti	Yes	No	No	No

As nouns, mufti is a hyponym of plain clothes; that is, mufti is a word with a more specific, narrower meaning than plain clothes:

plain clothes: ordinary clothing as distinguished from uniforms, work clothes, clerical garb, etc.
mufti: civilian dress worn by a person who is entitled to wear a military uniform

Other hyponyms of plain clothes include civies, civvies.

plain clothes (noun)	mufti (noun)
ordinary clothing as distinguished from uniforms, work clothes, clerical garb, etc.	civilian dress worn by a person who is entitled to wear a military uniform
	a jurist who interprets Muslim religious law