Source : Webster's Revised Unabridged Dictionary (1913)

Declivitous \De*cliv"i*tous\, Declivous \De*cli"vous\, a.
   Descending gradually; moderately steep; sloping; downhill.

Source : WordNet®

declivitous
     adj : sloping down rather steeply [syn: {downhill}, {downward-sloping}]