The Collaborative International Dictionary of English v.0.48:

Stop \Stop\, n.
   1. The act of stopping, or the state of being stopped;
      hindrance of progress or of action; cessation; repression;
      interruption; check; obstruction.
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            It is doubtful . . . whether it contributed anything
            to the stop of the infection.         --De Foe.
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            Occult qualities put a stop to the improvement of
            natural philosophy.                   --Sir I.
                                                  Newton.
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            It is a great step toward the mastery of our desires
            to give this stop to them.            --Locke.
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   2. That which stops, impedes, or obstructs; as obstacle; an
      impediment; an obstruction.
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            A fatal stop traversed their headlong course.
                                                  --Daniel.
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            So melancholy a prospect should inspire us with zeal
            to oppose some stop to the rising torrent. --Rogers.
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   3. (Mach.) A device, or piece, as a pin, block, pawl, etc.,
      for arresting or limiting motion, or for determining the
      position to which another part shall be brought.
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   4. (Mus.)
      (a) The closing of an aperture in the air passage, or
          pressure of the finger upon the string, of an
          instrument of music, so as to modify the tone; hence,
          any contrivance by which the sounds of a musical
          instrument are regulated.
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                The organ sound a time survives the stop.
                                                  --Daniel.
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      (b) In the organ, one of the knobs or handles at each side
          of the organist, by which he can draw on or shut off
          any register or row of pipes; the register itself; as,
          the vox humana stop.
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   5. (Arch.) A member, plain or molded, formed of a separate
      piece and fixed to a jamb, against which a door or window
      shuts. This takes the place, or answers the purpose, of a
      rebate. Also, a pin or block to prevent a drawer from
      sliding too far.
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   6. A point or mark in writing or printing intended to
      distinguish the sentences, parts of a sentence, or
      clauses; a mark of punctuation. See Punctuation.
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   7. (Opt.) The diaphragm used in optical instruments to cut
      off the marginal portions of a beam of light passing
      through lenses.
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   8. (Zool.) The depression in the face of a dog between the
      skull and the nasal bones. It is conspicuous in the
      bulldog, pug, and some other breeds.
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   9. (Phonetics) Some part of the articulating organs, as the
      lips, or the tongue and palate, closed
      (a) so as to cut off the passage of breath or voice
          through the mouth and the nose (distinguished as a
          lip-stop, or a front-stop, etc., as in p, t, d, etc.),
          or
      (b) so as to obstruct, but not entirely cut off, the
          passage, as in l, n, etc.; also, any of the consonants
          so formed. --H. Sweet.
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   Stop bead (Arch.), the molding screwed to the inner side of
      a window frame, on the face of the pulley stile,
      completing the groove in which the inner sash is to slide.


   Stop motion (Mach.), an automatic device for arresting the
      motion of a machine, as when a certain operation is
      completed, or when an imperfection occurs in its
      performance or product, or in the material which is
      supplied to it, etc.

   Stop plank, one of a set of planks employed to form a sort
      of dam in some hydraulic works.

   Stop valve, a valve that can be closed or opened at will,
      as by hand, for preventing or regulating flow, as of a
      liquid in a pipe; -- in distinction from a valve which is
      operated by the action of the fluid it restrains.

   Stop watch, a watch the hands of which can be stopped in
      order to tell exactly the time that has passed, as in
      timing a race. See Independent seconds watch, under
      Independent, a.
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   Syn: Cessation; check; obstruction; obstacle; hindrance;
        impediment; interruption.
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WordNet (r) 3.0 (2006):

stop watch
    n 1: a timepiece that can be started or stopped for exact timing
         (as of a race) [syn: stopwatch, stop watch]