plainclothesman

or plain·clothes man

[pleyn-klohz-muh n, -man, -klohth z-]

noun, plural plain·clothes·men

[pleyn-klohz-muh n, -men, -klohth z-] /ˈpleɪnˈkloʊz mən, -ˌmɛn, -ˈkloʊðz-/.

a police officer, especially a detective, who wears ordinary civilian clothes while on duty.

Origin of plainclothesman

First recorded in 1925–30; plain clothes + man¹

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for plainclothesman

Historical Examples of plainclothesman

A plainclothesman put a stethoscope on the questionable case.
The Pirates of Ersatz
Murray Leinster
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.
The Pirates of Ersatz
Murray Leinster
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