Source : Webster's Revised Unabridged Dictionary (1913)

Perpendicular \Per`pen*dic"u*lar\, n.
   1. A line at right angles to the plane of the horizon; a
      vertical line or direction.

   2. (Geom.) A line or plane falling at right angles on another
      line or surface, or making equal angles with it on each
      side.

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
     adj 1: intersecting at or forming right angles; "the axes are
            perpendicular to each other" [ant: {oblique}, {parallel}]
     2: at right angles to the plane of the horizon or a base line;
        "a vertical camera angle"; "the monument consists of two
        vertical pillars supporting a horizontal slab"; "measure
        the perpendicular height" [syn: {vertical}] [ant: {inclined},
         {horizontal}]
     3: extremely steep; "the great perpendicular face of the cliff"

perpendicular
     n 1: a straight line at right angles to another line
     2: a Gothic style in 14th and 15th century England;
        characterized by vertical lines and a four-centered
        (Tudor) arch and fan vaulting [syn: {perpendicular style},
         {English-Gothic}, {English-Gothic architecture}]
     3: a cord from which a metal weight is suspended pointing
        directly to the earth's center of gravity; used to
        determine the vertical from a given point [syn: {plumb
        line}]
     4: an extremely steep face