plain·clothes 
/ˈpleɪnˈkloʊz/ adjective
always used before a noun /ˈpleɪnˈkloʊz/ adjective : dressed in ordinary clothes and not a uniform while on duty
▪ a plainclothes police officer — see also plain clothes at 1plain
▪ a plainclothes police officer — see also plain clothes at 1plain
