[shirt.sleeve] n (ca. 1566): the sleeve of a shirt -- in shirtsleeves : wearing a shirt but no coat
[2]shirtsleeve also shirt.sleeves or shirt.sleeved adj (1864) 1 a: being without a coat "a ~ spectator" b: calling for the removal of coats for the sake of comfort or efficiency "~ weather"
2: marked by informality and directness "~ diplomacy"