Source : Webster's Revised Unabridged Dictionary (1913)

Deadhead \Dead"head`\, n.
   1. One who receives free tickets for theaters, public
      conveyances, etc. [Colloq. U. S.]

   2. (Naut.) A buoy. See under {Dead}, a.

Source : WordNet®

deadhead
     n 1: a nonenterprising person who is not paying his way; "the
          deadheads on the payroll should be eased out as fast as
          possible"
     2: a train or bus or taxi traveling empty