noun
plainclothes police officer; plain-clothes detective
Refers to a police officer or detective who works in civilian clothes rather than a uniform. Often used in crime fiction and news reports.
See also: 私服警官
私服刑事が繁華街で張り込みをしていた。
A plainclothes detective was on a stakeout in the downtown area.
彼は私服刑事だと気づかれずに容疑者に近づいた。
He approached the suspect without being noticed as a plainclothes officer.