The Collaborative International Dictionary of English v.0.48:

Monkey \Mon"key\, n.; pl. Monkeys. [Cf. OIt. monicchio, It.
   monnino, dim. of monna an ape, also dame, mistress, contr.
   fr. madonna. See Madonna.]
   1. (Zool.)
      (a) In the most general sense, any one of the Quadrumana,
          including apes, baboons, and lemurs.
      (b) Any species of Quadrumana, except the lemurs.
      (c) Any one of numerous species of Quadrumana (esp. such
          as have a long tail and prehensile feet) exclusive of
          apes and baboons.
          [1913 Webster]

   Note: The monkeys are often divided into three groups: (a)
         Catarrhines, or Simidae. These have an oblong head,
         with the oblique flat nostrils near together. Some have
         no tail, as the apes. All these are natives of the Old
         World. (b) Platyrhines, or Cebidae. These have a
         round head, with a broad nasal septum, so that the
         nostrils are wide apart and directed downward. The tail
         is often prehensile, and the thumb is short and not
         opposable. These are natives of the New World. (c)
         Strepsorhines, or Lemuroidea. These have a pointed
         head with curved nostrils. They are natives of Southern
         Asia, Africa, and Madagascar.
         [1913 Webster]

   2. A term of disapproval, ridicule, or contempt, as for a
      mischievous child.
      [1913 Webster]

            This is the monkey's own giving out; she is
            persuaded I will marry her.           --Shak.
      [1913 Webster]

   3. The weight or hammer of a pile driver, that is, a very
      heavy mass of iron, which, being raised on high, falls on
      the head of the pile, and drives it into the earth; the
      falling weight of a drop hammer used in forging.
      [1913 Webster]

   4. A small trading vessel of the sixteenth century.
      [1913 Webster]

   Monkey boat. (Naut.)
      (a) A small boat used in docks.
      (b) A half-decked boat used on the River Thames.

   Monkey block (Naut.), a small single block strapped with a
      swivel. --R. H. Dana, Jr.

   Monkey flower (Bot.), a plant of the genus Mimulus; -- so
      called from the appearance of its gaping corolla. --Gray.

   Monkey gaff (Naut.), a light gaff attached to the topmast
      for the better display of signals at sea.

   Monkey jacket, a short closely fitting jacket, worn by
      sailors.

   Monkey rail (Naut.), a second and lighter rail raised about
      six inches above the quarter rail of a ship.

   Monkey shine, monkey trick. [Slang, U.S.]

   Monkey trick, a mischievous prank. --Saintsbury.

   Monkey wheel. See Gin block, under 5th Gin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

monkey jacket
    n 1: waist-length jacket tapering to a point at the back; worn
         by officers in the mess for formal dinners [syn: mess
         jacket, monkey jacket, shell jacket]