declivous
descending
collapsing
deciduous
declined
declining
declivate
decurrent
descendant
dipping
down
down-reaching
downcoming
downfalling
downgoing
downgrade
downhill
downsinking
downward
drooping
dropping
falling
inclining
leaning
oblique
on the descendant
on the downgrade
pitched
plummeting
plunging
sagging
setting
sinking
sloped
sloping
steep
submerging
subsiding
tilted
tipped
tottering
tumbledown