The Collaborative International Dictionary of English v.0.48:

Ruler \Rul"er\ (r[udd]l"[~e]r), n.
   1. One who rules; one who exercises sway or authority; a
      governor.
      [1913 Webster]

            And he made him ruler over all the land. --Gen. xli.
                                                  43.
      [1913 Webster]

            A prince and ruler of the land.       --Shak.
      [1913 Webster]

   2. A straight or curved strip of wood, metal, etc., with a
      smooth edge, used for guiding a pen or pencil in drawing
      lines. Cf. Rule, n., 7
      (a) .
          [1913 Webster]

   Parallel ruler. See under Parallel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ruler
    n 1: a person who rules or commands; "swayer of the universe"
         [syn: ruler, swayer]
    2: measuring stick consisting of a strip of wood or metal or
       plastic with a straight edge that is used for drawing
       straight lines and measuring lengths [syn: rule, ruler]