The Collaborative International Dictionary of English v.0.48:

Slope \Slope\, v. t. [imp. & p. p. Sloped; p. pr. & vb. n.
   Sloping.]
   To form with a slope; to give an oblique or slanting
   direction to; to direct obliquely; to incline; to slant; as,
   to slope the ground in a garden; to slope a piece of cloth in
   cutting a garment.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sloping \Slop"ing\, a.
   Inclining or inclined from the plane of the horizon, or from
   a horizontal or other right line; oblique; declivous;
   slanting. -- Slop"ing*ly, adv.
   [1913 Webster]

         The sloping land recedes into the clouds. --Cowper.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sloping
    adj 1: having an oblique or slanted direction [syn: aslant,
           aslope, diagonal, slanted, slanting, sloped,
           sloping]
    2: having a slanting form or direction; "an area of gently
       sloping hills"; "a room with a sloping ceiling"

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "sloping":
   aslant, aslope, atilt, bevel, beveled, bias, biased, canting,
   careening, inclinational, inclinatory, inclined, inclining,
   leaning, listing, oblique, out of plumb, out of square, pitched,
   pitching, raking, recumbent, shelving, shelvy, sideling, sidelong,
   slant, slanted, slanting, slantways, slantwise, sloped, tilted,
   tilting, tipped, tipping, tipsy