In a manner that slopes downward or declines; moving or arranged in a way that goes down.
From declivity (Latin declivitas, from declivis 'sloping down') plus -ously, forming an adverb from the adjective declivitous. The Latin root breaks into de- (down) and clivus (slope/hill).
This beautifully precise word captures something we experience constantly—the slope of a hillside or the way a path descends—yet most people don't have a single word for it. Ancient Roman engineers would have used declivity constantly when building roads and aqueducts.
Complete word intelligence in one call. Free tier — 50 lookups/day.