The Collaborative International Dictionary of English v.0.48:

Turning \Turn"ing\, n.
   1. The act of one who, or that which, turns; also, a winding;
      a bending course; a flexure; a meander.
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            Through paths and turnings often trod by day.
                                                  --Milton.
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   2. The place of a turn; an angle or corner, as of a road.
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            It is preached at every turning.      --Coleridge.
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   3. Deviation from the way or proper course. --Harmar.
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   4. Turnery, or the shaping of solid substances into various
      forms by means of a lathe and cutting tools.
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   5. pl. The pieces, or chips, detached in the process of
      turning from the material turned; -- usually used in the
      plural.
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   6. (Mil.) A maneuver by which an enemy or a position is
      turned.
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   Turning and boring mill, a kind of lathe having a vertical
      spindle and horizontal face plate, for turning and boring
      large work.

   Turning bridge. See the Note under Drawbridge.

   Turning engine, an engine lathe.

   Turning lathe, a lathe used by turners to shape their work.


   Turning pair. See the Note under Pair, n.

   Turning point, the point upon which a question turns, and
      which decides a case.
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WordNet (r) 3.0 (2006):

turning point
    n 1: an event marking a unique or important historical change of
         course or one on which important developments depend; "the
         agreement was a watershed in the history of both nations"
         [syn: landmark, turning point, watershed]
    2: the intersection of two streets; "standing on the corner
       watching all the girls go by" [syn: corner, street
       corner, turning point]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "turning point":
   bench mark, cardinal point, chief thing, climacteric, climax,
   clutch, contingency, convergence of events, core, cornerstone,
   crisis, critical juncture, critical point, crossroads,
   crucial period, crunch, crux, culmination, emergency, essence,
   essential, essential matter, exigency, extremity, fundamental,
   gist, gravamen, great point, heart, high point, hinge,
   important thing, issue, kernel, keystone, landmark, main point,
   main thing, material point, meat, milestone, moment of truth, nub,
   pass, peak, pinch, pith, pivot, push, real issue, rub,
   salient point, sine qua non, strait, substance, substantive point,
   the bottom line, the point, turn, zero hour