The sleeve of a shirt. 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. also (-slē vd′) Dressed without a coat: shirtsleeve spectators; a shirtsleeved orchestra. also Calling for the removal of a coat or jacket; not requiring a coat or jacket for comfort: shirtsleeve weather; a shirtsleeves picnic. also Marked by informality or straightforwardness: shirtsleeve politics; a shirtsleeves conference.