[syn: vertical, perpendicular]
3.  extremely steep; 
- Example: "the great perpendicular face of the cliff"
The Collaborative International Dictionary of English v.0.48:
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.
      [1913 Webster]
   2. (Geom.) At right angles to a given line or surface; as,
      the line ad is perpendicular to the line bc.
      [1913 Webster]
   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.
      [1913 Webster]
The Collaborative International Dictionary of English v.0.48:
Perpendicular \Per`pen*dic"u*lar\, n.
   1. A line at right angles to the plane of the horizon; a
      vertical line or direction.
      [1913 Webster]
   2. (Geom.) A line or plane falling at right angles on another
      line or surface, or making equal angles with it on each
      side.
      [1913 Webster]
WordNet (r) 3.0 (2006):
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, perpendicular]
       [ant: horizontal, inclined]
    3: extremely steep; "the great perpendicular face of the cliff"
    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, 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,
       perpendicular]
    4: an extremely steep face
Moby Thesaurus II by Grady Ward, 1.0:
49 Moby Thesaurus words for "perpendicular":
   air line, axis, azimuth circle, beeline, chord, diagonal, diameter,
   direct line, directrix, edge, erect, great-circle course, normal,
   orthodiagonal, orthogonal, orthometric, plumb, plunging,
   precipitous, radius, radius vector, rectangular, right angle,
   right line, right-angle, right-angled, right-angular, secant,
   segment, sheer, shortcut, side, stand-up, steep, straight,
   straight course, straight line, straight stretch, straight-up,
   straight-up-and-down, straightaway, streamline, tangent,
   transversal, up-and-down, upright, vector, vertical,
   vertical circle