The Collaborative International Dictionary of English v.0.48:

Truncheon \Trun"cheon\, v. t.
   To beat with a truncheon. --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Truncheon \Trun"cheon\, n. [OE. tronchoun the shaft of a broken
   spear, broken piece, OF. tronchon, tron?on, F. tron?on, fr.
   OF. & F. tronce, tronche, a piece of wood; cf. OF. trons,
   tros, trois; all perhaps from L. thyrsus a stalk, stem,
   staff. See Thyrsus, and cf. Trounce.]
   1. A short staff, a club; a cudgel; a shaft of a spear.
      [1913 Webster]

            With his truncheon he so rudely struck. --Spenser.
      [1913 Webster]

   2. A baton, or military staff of command.
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            The marshal's truncheon nor the judges robe. --Shak.
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   3. A stout stem, as of a tree, with the branches lopped off,
      to produce rapid growth. --Gardner.
      [1913 Webster]

WordNet (r) 3.0 (2006):

truncheon
    n 1: a short stout club used primarily by policemen [syn:
         truncheon, nightstick, baton, billy, billystick,
         billy club]