shirt sleeves noun[plural only]2 •Preceded by in: wearing only a shirt without a coat, jacket, or comparable protective covering over it.A bunch of workmen were lying on the grass of the park beside Macquarie Street, in the dinner hour. It was winter, the end of May, but the sun was warm, and they lay there in shirt-sleeves, talking. — 1923 •A working-class socioeconomic status (not requiring a professional business jacket).
