Synonyms and related words :
collapsing, deciduous, declining, declivitous, decurrent, descendant, descending, down, down-reaching, downcoming, downfalling, downgoing, downhill, downsinking, downward, drooping, dropping, falling, on the descendant, on the downgrade, plummeting, plunging, sagging, setting, sinking, submerging, subsiding, tottering, tumbledown