plainclothesman vs detective

plainclothesman and detective both are nouns.

Word	Noun	Adjective	Verb	Adverb
plainclothesman	Yes	No	No	No
detective	Yes	No	No	No

As nouns, detective is a hypernym of plainclothesman; that is, detective is a word with a broader meaning than plainclothesman:

Other hypernyms of plainclothesman include investigator, police detective, tec.

plainclothesman (noun)	detective (noun)
a detective who wears civilian clothes on duty	a police officer who investigates crimes
	an investigator engaged or employed in obtaining information not easily available to the public