The Collaborative International Dictionary of English v.0.48:

Crotchet \Crotch"et\ (kr?ch"?t; 224), n. [F. crochet, prop., a
   little hook, a dim. from the same source as croc hook. See
   Crook, and cf. Crochet, Crocket, Crosier.]
   1. A forked support; a crotch.
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            The crotchets of their cot in columns rise.
                                                  --Dryden.
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   2. (Mus.) A time note, with a stem, having one fourth the
      value of a semibreve, one half that of a minim, and twice
      that of a quaver; a quarter note.
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   3. (Fort.) An indentation in the glacis of the covered way,
      at a point where a traverse is placed.
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   4. (Mil.) The arrangement of a body of troops, either forward
      or rearward, so as to form a line nearly perpendicular to
      the general line of battle.
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   5. (Print.) A bracket. See Bracket.
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   6. (Med.) An instrument of a hooked form, used in certain
      cases in the extraction of a fetus. --Dunglison.
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   7. A perverse fancy; a whim which takes possession of the
      mind; a conceit.
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            He ruined himself and all that trusted in him by
            crotchets that he could never explain to any
            rational man.                         --De Quincey.
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The Collaborative International Dictionary of English v.0.48:

Crotchet \Crotch"et\, v. i.
   To play music in measured time. [Obs.] --Donne.
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The Collaborative International Dictionary of English v.0.48:

Bracket \Brack"et\, n. [Cf. OF. braguette codpiece, F. brayette,
   Sp. bragueta, also a projecting mold in architecture; dim.
   fr. L. bracae breeches; cf. also, OF. bracon beam, prop,
   support; of unknown origin. Cf. Breeches.]
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   1. (Arch.) An architectural member, plain or ornamental,
      projecting from a wall or pier, to support weight falling
      outside of the same; also, a decorative feature seeming to
      discharge such an office.
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   Note: This is the more general word. See Brace,
         Cantalever, Console, Corbel, Strut.
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   2. (Engin. & Mech.) A piece or combination of pieces, usually
      triangular in general shape, projecting from, or fastened
      to, a wall, or other surface, to support heavy bodies or
      to strengthen angles.
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   3. (Naut.) A shot, crooked timber, resembling a knee, used as
      a support.
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   4. (Mil.) The cheek or side of an ordnance carriage.
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   5. (Print.) One of two characters [], used to inclose a
      reference, explanation, or note, or a part to be excluded
      from a sentence, to indicate an interpolation, to rectify
      a mistake, or to supply an omission, and for certain other
      purposes; -- called also crotchet.
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   6. A gas fixture or lamp holder projecting from the face of a
      wall, column, or the like.
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   7. (Gunnery) A figure determined by firing a projectile
      beyond a target and another short of it, as a basis for
      ascertaining the proper elevation of the piece; -- only
      used in the phrase, to establish a bracket. After the
      bracket is established shots are fired with intermediate
      elevations until the exact range is obtained. In the
      United States navy it is called fork.
      [Webster 1913 Suppl.]

   Bracket light, a gas fixture or a lamp attached to a wall,
      column, etc.
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WordNet (r) 3.0 (2006):

crotchet
    n 1: a sharp curve or crook; a shape resembling a hook [syn:
         hook, crotchet]
    2: a musical note having the time value of a quarter of a whole
       note [syn: quarter note, crotchet]
    3: a strange attitude or habit [syn: oddity, queerness,
       quirk, quirkiness, crotchet]
    4: a small tool or hooklike implement