a police officer, especially a detective, who wears ordinary civilian clothes while on duty.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use plainclothesman in a sentence
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
Were they with some policeman as they came out of the building or in custody of some plainclothesman?Warren Commission (3 of 26): Hearings Vol. III (of 15) | The President's Commission on the Assassination of President Kennedy
She smiled in silent gratitude and allowed the plainclothesman to lead her away from that chamber of horror.
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