plainclothesman

or plain·clothes man

[pleyn-klohz-muh n, -man, -klohth z-]
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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. 2019

Examples from the Web for plainclothesman

Historical Examples of plainclothesman