ETYM Old Eng. tronchoun the shaft of a broken spear, broken piece, Old Fren. tronchon, tronçon, French tronçon, from Old Fren. and French tronce, tronche, a piece of wood.
Broken spear; broken or cut piece.
A policeman's club; SYN. nightstick, billy, billystick, stick.

To beat with a truncheon