The Collaborative International Dictionary of English v.0.48:

Lug \Lug\ (l[u^]g), n. [Sw. lugg the forelock.]
   1. The ear, or its lobe. [Scot. & Prov. Eng.]
      [1913 Webster]

   2. That which projects like an ear, esp. that by which
      anything is supported, carried, or grasped, or to which a
      support is fastened; an ear; as, the lugs of a kettle; the
      lugs of a founder's flask; the lug (handle) of a jug.
      [1913 Webster]

   3. (Mach.) A projecting piece to which anything, as a rod, is
      attached, or against which anything, as a wedge or key,
      bears, or through which a bolt passes, etc.
      [1913 Webster]

   4. (Harness) The leather loop or ear by which a shaft is held
      up.
      [1913 Webster]

   5. (Zool.) The lugworm.
      [1913 Webster]

   6. A man; sometimes implying clumsiness. [slang]
      [PJC]

   Lug bolt (Mach.), a bolt terminating in a long, flat
      extension which takes the place of a head; a strap bolt.


   Lug nut (Mach.), a large nut fitting a heavy bolt; -- used
      especially of the nuts used to attach wheels to vehicles.


   Lug wrench (Mach.), a wrench used to tighten or loosen lug
      nuts, usually a steel rod having a hexagonally shaped
      socket which fits closely over the lug nut; sometimes in
      the shape of a cross, having several such sockets, one at
      the end of each arm, to accommodate nuts of different
      sizes.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

lug wrench
    n 1: a wrench with jaws that have projecting lugs to engage the
         object that is to be rotated