Plainclothesman (noun)

A police officer who is dressed in civilian clothes to avoid detection while working on undercover operations or investigations.

Origin:

First recorded use of the term 'plainclothesman' was in 1844, derived from the adjective 'plainclothes' which refers to clothing worn by someone who is not wearing a uniform.

Examples:

1. The plainclothesman was able to gather important information about the criminal gang by infiltrating their meetings.
2. The robbers never suspected that the man sitting next to them in the coffee shop was actually a plainclothesman.
3. The plainclothesman was able to solve the case by posing as a customer in the shady bar.
4. The plainclothesman's cover was blown when a fellow officer recognized him during the investigation.
5. The plainclothesman was recognized by one of the suspects but he was able to keep up his cover and continue the investigation.