The Collaborative International Dictionary of English v.0.48:

Peg \Peg\ (p[e^]g), n. [OE. pegge; cf. Sw. pigg, Dan. pig a
   point, prickle, and E. peak.]
   1. A small, pointed piece of wood, used in fastening boards
      together, in attaching the soles of boots or shoes, etc.;
      as, a shoe peg.
      [1913 Webster]

   2. A wooden pin, or nail, on which to hang things, as coats,
      etc. Hence, colloquially and figuratively: A support; a
      reason; a pretext; as, a peg to hang a claim upon.
      [1913 Webster]

   3. One of the pins of a musical instrument, on which the
      strings are strained. --Shak.
      [1913 Webster]

   4. One of the pins used for marking points on a cribbage
      board.
      [1913 Webster]

   5. A step; a degree; esp. in the slang phrase "To take one
      down a peg."
      [1913 Webster]

            To screw papal authority to the highest peg.
                                                  --Barrow.
      [1913 Webster]

            And took your grandees down a peg.    --Hudibras.
      [1913 Webster]

   6. A drink of spirits, usually whisky or brandy diluted with
      soda water. [India]

            This over, the club will be visited for a "peg,"
            Anglice drink.                        --Harper's
                                                  Mag.
      [Webster 1913 Suppl.]

   7. (Baseball) a hard throw, especially one made to put out a
      baserunner; as, the peg to the plate went wild.
      [PJC]

   peg board, a board with multiple small holes into which
      pegs can be inserted in different arrays so as to form
      hooks from which to hang tools or other objects for
      convenient access; it is typically hung from a wall in a
      workshop.

   Peg ladder, a ladder with but one standard, into which
      cross pieces are inserted.

   Peg tankard, an ancient tankard marked with pegs, so as
      divide the liquor into equal portions. "Drink down to your
      peg." --Longfellow.

   Peg tooth. See Fleam tooth under Fleam.

   Peg top, a boy's top which is spun by throwing it.

   Screw peg, a small screw without a head, for fastening
      soles.
      [1913 Webster +PJC]