n. The sleeve of a shirt.n. The state of wearing no coat, jacket, or other outer garment over one's shirt: dined in shirtsleeves; balmy weather that had them down to their shirtsleeves. adj. Dressed without a coat: shirtsleeve spectators; a shirtsleeved orchestra. adj. Calling for the removal of a coat or jacket; not requiring a coat or jacket for comfort: shirtsleeve weather; a shirtsleeves picnic. adj. Marked by informality or straightforwardness: shirtsleeve politics; a shirtsleeves conference.