Synonyms of 'declivity'
the angular distance, esp in degrees, of a star, planet, etc, from the celestial equator measured north (positive) or south (negative) along the great circle passing through the celestial poles and the body
A descent is a surface that slopes downwards, for example the side of a steep hill.
On the descents, cyclists freewheel past cars.
Thesaurus for declivity from the Collins English Thesaurus
a downward slope , esp of the ground