or plain·clothes man
noun, plural plain·clothes·men [pleyn-klohz-muh n, -men, -klohth z-] /ˈpleɪnˈkloʊz mən, -ˌmɛn, -ˈkloʊðz-/.
Origin of plainclothesman
Examples from the Web for plainclothesman
Historical Examples of plainclothesman
A plainclothesman put a stethoscope on the questionable case.
The police sergeant and plainclothesman exchanged a quick glance.Dan Carter and the River Camp
Mildred A. Wirt
The other plainclothesman came up to Sergeant Ketzel and Bending as they entered.Damned If You Don't
Gordon Randall Garrett
He lingered, but the plainclothesman was staring at the innocent, inviolable parcels about to leave the Embassy for distant parts.
Yes, plainclothesman, wearing black hats; one of them had one of those Texas hats.Warren Commission (2 of 26): Hearings Vol. II (of 15)
The President's Commission on the Assassination of President Kennedy