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):

slopingly
    adv 1: with a slant [syn: slantingly, slopingly]