The Collaborative International Dictionary of English v.0.48:

Driver \Driv"er\, n. [From Drive.]
   1. One who, or that which, drives; the person or thing that
      urges or compels anything else to move onward.
      [1913 Webster]

   2. The person who drives beasts or a carriage; a coachman; a
      charioteer, etc.; hence, also, one who controls the
      movements of a any vehicle.
      [1913 Webster +PJC]

   3. An overseer of a gang of slaves or gang of convicts at
      their work.
      [1913 Webster]

   4. (Mach.) A part that transmits motion to another part by
      contact with it, or through an intermediate relatively
      movable part, as a gear which drives another, or a lever
      which moves another through a link, etc. Specifically:
      (a) The driving wheel of a locomotive.
      (b) An attachment to a lathe, spindle, or face plate to
          turn a carrier.
      (c) A crossbar on a grinding mill spindle to drive the
          upper stone.
          [1913 Webster]

   5. (Naut.) The after sail in a ship or bark, being a
      fore-and-aft sail attached to a gaff; a spanker. --Totten.
      [1913 Webster]

   6. An implement used for driving; as:
      (a) A mallet.
      (b) A tamping iron.
      (c) A cooper's hammer for driving on barrel hoops.
      (d) A wooden-headed golf club with a long shaft, for
          playing the longest strokes.
          [Webster 1913 Suppl.]

   Driver ant (Zool.), a species of African stinging ant; one
      of the visiting ants (Anomma arcens); -- so called
      because they move about in vast armies, and drive away or
      devour all insects and other small animals.
      [1913 Webster]

WordNet (r) 3.0 (2006):

driver ant
    n 1: tropical nomadic ant that preys mainly on other insects
         [syn: army ant, driver ant, legionary ant]