Source : Webster's Revised Unabridged Dictionary (1913)

Protractor \Pro*tract"or\, n.
   1. One who, or that which, protracts, or causes protraction.

   2. A mathematical instrument for laying down and measuring
      angles on paper, used in drawing or in plotting. It is of
      various forms, semicircular, rectangular, or circular.

   3. (Surg.) An instrument formerly used in extracting foreign
      or offensive matter from a wound.

   4. (Anat.) A muscle which extends an organ or part; --
      opposed to {retractor}.

   5. An adjustable pattern used by tailors. --Knight.

Source : WordNet®

protractor
     n : drafting instrument used to draw or measure angles