From The Collaborative International Dictionary of English v.0.48 :
downslope \downslope\ n.
a downward slope.
Syn: descent, declivity, fall, decline.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
downslope
n 1: a downward slope or bend [syn: descent, declivity,
fall, decline, declination, declension,
downslope] [ant: acclivity, ascent, climb, raise,
rise, upgrade]