DECLIVITY
descent, declivity, fall, decline, declination, declension, downslope
(noun) a downward slope or bend
Source: WordNet® 3.1
Etymology
Noun
declivity (plural declivities)
(geomorphology) The downward slope of a hill; the downward slope of a curve.
A downward bend in a path.
(entomology) An inward curve of the exoskeleton of an insect, such as between body segments; a segment of an insect's body where the exoskeleton curves inward.
Source: Wiktionary
De*cliv"i*ty, n.; pl. Declivities. Etym: [L. declivitas, fr. declivis
sloping, downhill; de + clivus a slope, a hill; akin to clinare to
incline: cf. F. déclivité. See Decline.]
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.
Source: Webster’s Unabridged Dictionary 1913 Edition