The Collaborative International Dictionary of English v.0.48:

Bonnet \Bon"net\ (b[o^]n"n[e^]t), n. [OE. bonet, OF. bonet,
   bonete. F. bonnet fr. LL. bonneta, bonetum; orig. the name of
   a stuff, and of unknown origin.]
   1. A headdress for men and boys; a cap. [Obs.] --Milton.
      --Shak.
      [1913 Webster]

   2. A soft, elastic, very durable cap, made of thick, seamless
      woolen stuff, and worn by men in Scotland.
      [1913 Webster]

            And plaids and bonnets waving high.   --Sir W.
                                                  Scott.
      [1913 Webster]

   3. A covering for the head, worn by women, usually protecting
      more or less the back and sides of the head, but no part
      of the forehead. The shape of the bonnet varies greatly at
      different times; formerly the front part projected, and
      spread outward, like the mouth of a funnel.
      [1913 Webster]

   4. Anything resembling a bonnet in shape or use; as,
      (a) (Fort.) A small defense work at a salient angle; or a
          part of a parapet elevated to screen the other part
          from enfilade fire.
      (b) A metallic canopy, or projection, over an opening, as
          a fireplace, or a cowl or hood to increase the draught
          of a chimney, etc.
      (c) A frame of wire netting over a locomotive chimney, to
          prevent escape of sparks.
      (d) A roofing over the cage of a mine, to protect its
          occupants from objects falling down the shaft.
      (e) In pumps, a metal covering for the openings in the
          valve chambers.
          [1913 Webster]

   5. (Naut.) An additional piece of canvas laced to the foot of
      a jib or foresail in moderate winds. --Hakluyt.
      [1913 Webster]

   6. The second stomach of a ruminating animal.
      [1913 Webster]

   7. An accomplice of a gambler, auctioneer, etc., who entices
      others to bet or to bid; a decoy. [Cant]
      [1913 Webster]

   8. (Automobiles) The metal cover or shield over the motor;
      predominantly British usage. In the U.S. it is called the
      hood. [Brit.]
      [Webster 1913 Suppl.]

   Bonnet limpet (Zool.), a name given, from their shape, to
      various species of shells (family Calyptr[ae]id[ae]).

   Bonnet monkey (Zool.), an East Indian monkey (Macacus
      sinicus), with a tuft of hair on its head; the munga.

   Bonnet piece, a gold coin of the time of James V. of
      Scotland, the king's head on which wears a bonnet. --Sir
      W. Scott.

   To have a bee in the bonnet. See under Bee.

   Black bonnet. See under Black.

   Blue bonnet. See in the Vocabulary.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bonnet \Bon"net\, v. i.
   To take off the bonnet or cap as a mark of respect; to
   uncover. [Obs.] --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bonnet
    n 1: a hat tied under the chin [syn: bonnet, poke bonnet]
    2: protective covering consisting of a metal part that covers
       the engine; "there are powerful engines under the hoods of
       new cars"; "the mechanic removed the cowling in order to
       repair the plane's engine" [syn: hood, bonnet, cowl,
       cowling]
    v 1: dress in a bonnet

Easton's 1897 Bible Dictionary:

Bonnet
   (Heb. peer), Ex. 39:28 (R.V., "head-tires"); Ezek. 44:18 (R.V.,
   "tires"), denotes properly a turban worn by priests, and in Isa.
   3:20 (R.V., "head-tires") a head-dress or tiara worn by females.
   The Hebrew word so rendered literally means an ornament, as in
   Isa. 61:10 (R.V., "garland"), and in Ezek. 24:17, 23 "tire"
   (R.V., "head-tire"). It consisted of a piece of cloth twisted
   about the head. In Ex. 28:40; 29:9 it is the translation of a
   different Hebrew word (migba'ah), which denotes the turban
   (R.V., "head-tire") of the common priest as distinguished from
   the mitre of the high priest. (See MITRE.)