The Collaborative International Dictionary of English v.0.48:

String \String\ (str[i^]ng), n. [OE. string, streng, AS. streng;
   akin to D. streng, G. strang, Icel. strengr, Sw. str[aum]ng,
   Dan. straeng; probably from the adj., E. strong (see
   Strong); or perhaps originally meaning, twisted, and akin
   to E. strangle.]
   1. A small cord, a line, a twine, or a slender strip of
      leather, or other substance, used for binding together,
      fastening, or tying things; a cord, larger than a thread
      and smaller than a rope; as, a shoe string; a bonnet
      string; a silken string. --Shak.
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            Round Ormond's knee thou tiest the mystic string.
                                                  --Prior.
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   2. A thread or cord on which a number of objects or parts are
      strung or arranged in close and orderly succession; hence,
      a line or series of things arranged on a thread, or as if
      so arranged; a succession; a concatenation; a chain; as, a
      string of shells or beads; a string of dried apples; a
      string of houses; a string of arguments. "A string of
      islands." --Gibbon.
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   3. A strip, as of leather, by which the covers of a book are
      held together. --Milton.
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   4. The cord of a musical instrument, as of a piano, harp, or
      violin; specifically (pl.), the stringed instruments of an
      orchestra, in distinction from the wind instruments; as,
      the strings took up the theme. "An instrument of ten
      strings." --Ps. xxx. iii. 2.
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            Me softer airs befit, and softer strings
            Of lute, or viol still.               --Milton.
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   5. The line or cord of a bow. --Ps. xi. 2.
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            He twangs the grieving string.        --Pope.
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   6. A fiber, as of a plant; a little, fibrous root.
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            Duckweed putteth forth a little string into the
            water, from the bottom.               --Bacon.
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   7. A nerve or tendon of an animal body.
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            The string of his tongue was loosed.  --Mark vii.
                                                  35.
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   8. (Shipbuilding) An inside range of ceiling planks,
      corresponding to the sheer strake on the outside and
      bolted to it.
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   9. (Bot.) The tough fibrous substance that unites the valves
      of the pericap of leguminous plants, and which is readily
      pulled off; as, the strings of beans.
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   10. (Mining) A small, filamentous ramification of a metallic
       vein. --Ure.
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   11. (Arch.) Same as Stringcourse.
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   12. (Billiards) The points made in a game.
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   13.
       (a) In various indoor games, a score or tally, sometimes,
           as in American billiard games, marked by buttons
           threaded on a string or wire.
       (b) In various games, competitions, etc., a certain
           number of turns at play, of rounds, etc.
           [Webster 1913 Suppl.]

   14. (Billiards & Pool)
       (a) The line from behind and over which the cue ball must
           be played after being out of play as by being
           pocketed or knocked off the table; -- called also
           string line.
       (b) Act of stringing for break.
           [Webster 1913 Suppl.]

   15. A hoax; a trumped-up or "fake" story. [Slang]
       [Webster 1913 Suppl.]

   16. a sequence of similar objects or events sufficiently
       close in time or space to be perceived as a group; a
       string of accidents; a string of restaurants on a
       highway.
       [PJC]

   17. (Physics) A one-dimensional string-like mathematical
       object used as a means of representing the properties of
       fundamental particles in string theory, one theory of
       particle physics; such hypothetical objects are
       one-dimensional and very small (10^-33 cm) but exist in
       more than four spatial dimensions, and have various modes
       of vibration. Considering particles as strings avoids
       some of the problems of treating particles as points, and
       allows a unified treatment of gravity along with the
       other three forces (electromagnetism, the weak force, and
       the strong force) in a manner consistent with quantum
       mechanics. See also string theory.
       [PJC]

   String band (Mus.), a band of musicians using only, or
      chiefly, stringed instruments.

   String beans.
       (a) A dish prepared from the unripe pods of several kinds
           of beans; -- so called because the strings are
           stripped off.
       (b) Any kind of beans in which the pods are used for
           cooking before the seeds are ripe; usually, the low
           bush bean.

   To have two strings to one's bow, to have a means or
      expedient in reserve in case the one employed fails.
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WordNet (r) 3.0 (2006):

string line
    n 1: line across a billiard table behind which the cue balls are
         placed at the start of a game [syn: balkline, baulk-
         line, string line]