The Collaborative International Dictionary of English v.0.48:

Pin \Pin\, n. [OE. pinne, AS. pinn a pin, peg; cf. D. pin, G.
   pinne, Icel. pinni, W. pin, Gael. & Ir. pinne; all fr. L.
   pinna a pinnacle, pin, feather, perhaps orig. a different
   word from pinna feather. Cf. Fin of a fish, Pen a
   feather.]
   1. A piece of wood, metal, etc., generally cylindrical, used
      for fastening separate articles together, or as a support
      by which one article may be suspended from another; a peg;
      a bolt.
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            With pins of adamant
            And chains they made all fast.        --Milton.
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   2. Especially, a small, pointed and headed piece of brass or
      other wire (commonly tinned), largely used for fastening
      clothes, attaching papers, etc.
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   3. Hence, a thing of small value; a trifle.
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            He . . . did not care a pin for her.  --Spectator.
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   4. That which resembles a pin in its form or use; as:
      (a) A peg in musical instruments, for increasing or
          relaxing the tension of the strings.
      (b) A linchpin.
      (c) A rolling-pin.
      (d) A clothespin.
      (e) (Mach.) A short shaft, sometimes forming a bolt, a
          part of which serves as a journal. See Illust. of
          Knuckle joint, under Knuckle.
      (f) (Joinery) The tenon of a dovetail joint.
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   5. One of a row of pegs in the side of an ancient drinking
      cup to mark how much each man should drink.
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   6. The bull's eye, or center, of a target; hence, the center.
      [Obs.] "The very pin of his heart cleft." --Shak.
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   7. Mood; humor. [Obs.] "In merry pin." --Cowper.
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   8. (Med.) Caligo. See Caligo. --Shak.
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   9. An ornament, as a brooch or badge, fastened to the
      clothing by a pin; as, a Masonic pin.
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   10. The leg; as, to knock one off his pins. [Slang]
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   Banking pin (Horol.), a pin against which a lever strikes,
      to limit its motion.

   Pin drill (Mech.), a drill with a central pin or projection
      to enter a hole, for enlarging the hole, or for sinking a
      recess for the head of a bolt, etc.; a counterbore.

   Pin grass. (Bot.) See Alfilaria.

   Pin hole, a small hole made by a pin; hence, any very small
      aperture or perforation.

   Pin lock, a lock having a cylindrical bolt; a lock in which
      pins, arranged by the key, are used instead of tumblers.


   Pin money, an allowance of money, as that made by a husband
      to his wife, for private and personal expenditure.

   Pin rail (Naut.), a rail, usually within the bulwarks, to
      hold belaying pins. Sometimes applied to the fife rail.
      Called also pin rack.

   Pin wheel.
       (a) A contrate wheel in which the cogs are cylindrical
           pins.
       (b) (Fireworks) A small coil which revolves on a common
           pin and makes a wheel of yellow or colored fire.
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