Source : Webster's Revised Unabridged Dictionary (1913)

Perpendicular \Per`pen*dic"u*lar\, a. [L. perpendicularis,
   perpendicularius: cf. F. perpendiculaire. See {Perpendicle},
   {Pension}.]
   1. Exactly upright or vertical; pointing to the zenith; at
      right angles to the plane of the horizon; extending in a
      right line from any point toward the center of the earth.

   2. (Geom.) At right angles to a given line or surface; as,
      the line ad is perpendicular to the line bc.

   {Perpendicular style} (Arch.), a name given to the latest
      variety of English Gothic architecture, which prevailed
      from the close of the 14th century to the early part of
      the 16th; -- probably so called from the vertical style of
      its window mullions.

Source : WordNet®

perpendicular style
     n : a Gothic style in 14th and 15th century England;
         characterized by vertical lines and a four-centered
         (Tudor) arch and fan vaulting [syn: {perpendicular}, {English-Gothic},
          {English-Gothic architecture}]