a garment for the upper body, usu one that opens the full length of the centre front and has sleeves and a collar
have/take the shirt off somebody's back
informal to take somebody's last remaining possessions
keep one's shirt on
informal to remain calm; not to lose one's temper
lose one's shirt
informal to lose a large amount of money or everything one has, esp in gambling
put one's shirt on
Brit, informal to bet all the money one has on (something)
Old English scyrte, related to Old Norse skyrta shirt, kirtle, ancestor of skirt1. Both prob come from the same prehistoric Germanic word as short1, literally meaning ‘short garment’