prettygoodword | truncheon

truncheon (TRUHN-chuhn) - n., a short club; esp. one formerly used as a military staff of command, now used a police officer's club or baton.

And just to get this out of the way, other terms for the police club include nightstick and lathi. This one goes back to the 14th century, in Middle English form tronchon/tronchoun, club, literally piece broken off, from Anglo-French trunchun, from Old French, from Vulgar Latin *trunciōn / *trunciō, literally a lopping, from Latin truncus, trunk.

a truncheon, also a nightstick, also a billy