The Collaborative International Dictionary of English v.0.48:

Guide \Guide\, n. [OE. giae, F. guide, It. guida. See Guide,
   v. t.]
   1. A person who leads or directs another in his way or
      course, as in a strange land; one who exhibits points of
      interest to strangers; a conductor; also, that which
      guides; a guidebook.
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   2. One who, or that which, directs another in his conduct or
      course of life; a director; a regulator.
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            He will be our guide, even unto death. --Ps. xlviii.
                                                  14.
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   3. Any contrivance, especially one having a directing edge,
      surface, or channel, for giving direction to the motion of
      anything, as water, an instrument, or part of a machine,
      or for directing the hand or eye, as of an operator; as:
      (a) (Water Wheels) A blade or channel for directing the
          flow of water to the wheel buckets.
      (b) (Surgery) A grooved director for a probe or knife.
      (c) (Printing) A strip or device to direct the
          compositor's eye to the line of copy he is setting.
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   4. (Mil.) A noncommissioned officer or soldier placed on the
      directing flank of each subdivision of a column of troops,
      or at the end of a line, to mark the pivots, formations,
      marches, and alignments in tactics. --Farrow.
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   Guide bar (Mach.), the part of a steam engine on which the
      crosshead slides, and by which the motion of the piston
      rod is kept parallel to the cylinder, being a substitute
      for the parallel motion; -- called also guide, and
      slide bar.

   Guide block (Steam Engine), a block attached in to the
      crosshead to work in contact with the guide bar.

   Guide meridian. (Surveying) See under Meridian.

   Guide pile (Engin.), a pile driven to mark a place, as a
      point to work to.

   Guide pulley (Mach.), a pulley for directing or changing
      the line of motion of belt; an idler. --Knight.

   Guide rail (Railroads), an additional rail, between the
      others, gripped by horizontal driving wheels on the
      locomotive, as a means of propulsion on steep gradients.
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