The Collaborative International Dictionary of English v.0.48:

nonparallel \nonparallel\ adj.
   1. not parallel; -- of lines or linear objects. Opposite of
      parallel. [Narrower terms: bias, catacorner,
      cata-cornered, catercorner, cater-cornered, catty-corner,
      catty-cornered, diagonal, kitty-corner, kitty-cornered,
      oblique, skew, skewed, slanted ; {crossed, decussate,
      intersectant, intersecting; cross-grained ; {diagonal;
      orthogonal, orthographic, rectangular, right-angled ;
      {right, perpendicular; angled ; {convergent] Also See:
      convergent, divergent, diverging.
      [WordNet 1.5]

   2. (Computers) Not using parallel processing; -- of
      computers. [Narrower terms: serial] PJC]

The Collaborative International Dictionary of English v.0.48:

Diagonal \Di*ag"o*nal\, a. [L. diagonalis, fr. Gr. ? from to
   angle; dia` through + ? an angle; perh. akin to E. knee: cf.
   F. diagonal.] (Geom.)
   Joining two not adjacent angles of a quadrilateral or
   multilateral figure; running across from corner to corner;
   crossing at an angle with one of the sides.
   [1913 Webster]

   Diagonal bond (Masonry), herringbone work. See
      Herringbone, a.

   Diagonal built (Shipbuilding), built by forming the outer
      skin of two layers of planking, making angles of about
      45[deg] with the keel, in opposite directions.

   Diagonal cleavage. See under Cleavage.

   Diagonal molding (Arch.), a chevron or zigzag molding.

   Diagonal rib. (Arch.) See Cross-springer.

   Diagonal scale, a scale which consists of a set of parallel
      lines, with other lines crossing them obliquely, so that
      their intersections furnish smaller subdivisions of the
      unit of measure than could be conveniently marked on a
      plain scale.

   Diagonal stratification. (Geol.) Same as Cross bedding,
      under Cross, a.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Diagonal \Di*ag"o*nal\, n.
   1. A right line drawn from one angle to another not adjacent,
      of a figure of four or more sides, and dividing it into
      two parts.
      [1913 Webster]

   2. (Engin.) A member, in a framed structure, running
      obliquely across a panel.
      [1913 Webster]

   3. A diagonal cloth; a kind of cloth having diagonal stripes,
      ridges, or welts made in the weaving.
      [1913 Webster]

WordNet (r) 3.0 (2006):

diagonal
    adj 1: connecting two nonadjacent corners of a plane figure or
           any two corners of a solid that are not in the same face;
           "a diagonal line across the page"
    2: having an oblique or slanted direction [syn: aslant,
       aslope, diagonal, slanted, slanting, sloped,
       sloping]
    n 1: (geometry) a straight line connecting any two vertices of a
         polygon that are not adjacent
    2: a line or cut across a fabric that is not at right angles to
       a side of the fabric [syn: diagonal, bias]
    3: an oblique line of squares of the same color on a
       checkerboard; "the bishop moves on the diagonals"
    4: (mathematics) a set of entries in a square matrix running
       diagonally either from the upper left to lower right entry or
       running from the upper right to lower left entry
    5: a punctuation mark (/) used to separate related items of
       information [syn: solidus, slash, virgule, diagonal,
       stroke, separatrix]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "diagonal":
   across, air line, athwart, axis, band, bar, beeline, bend,
   bendwise, bevel, beveled, bias, biased, biaswise, catercorner,
   catercornered, chord, cross-hatching, crossways, crosswise, dash,
   delineation, diameter, direct line, directrix, dotted line, edge,
   great-circle course, hachure, hairline, hatching, kittycorner,
   line, lineation, normal, oblique, oblique angle, oblique figure,
   oblique line, perpendicular, radius, radius vector, rhomboid,
   right line, score, scratch comma, secant, segment, separatrix,
   shortcut, side, slant, slanted, slanting, slash, solidus, straight,
   straight course, straight line, straight stretch, straightaway,
   streak, streaking, streamline, striation, strip, stripe, striping,
   stroke, sublineation, tangent, thwart, transversal, transverse,
   underline, underlining, underscore, underscoring, vector,
   virgule



U.S. Gazetteer Places (2000):

Diagonal, IA -- U.S. city in Iowa
   Population (2000):    312
   Housing Units (2000): 154
   Land area (2000):     0.908254 sq. miles (2.352367 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.908254 sq. miles (2.352367 sq. km)
   FIPS code:            21270
   Located within:       Iowa (IA), FIPS 19
   Location:             40.808819 N, 94.341510 W
   ZIP Codes (1990):     50845
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Diagonal, IA
    Diagonal