Declivity

Part of speech: noun (n.)

1. Deviation from a horizontal line; gradual descent of surface; inclination downward; slope; -- opposed to acclivity, or ascent; the same slope, considered as descending, being a declivity, which, considered as ascending, is an acclivity.

2. A descending surface; a sloping place. Commodious declivities and channels for the passage of the waters. Derham.