declivity

noun

1. The downward slope of a curve.

   “The Declivity was ſo ſmall, that I walked near a mile before I got to the Shore, which I conjectur'd was about eight a-clock in the Evening.”

   “1780, Theodore Augustine Mann, A Treatise on Rivers and Canals, Philosophical Transactions of the Royal Society of London, Volume 69: For the Year 1779, Part II, 582, The velocity of flowing waters is very far from being in proportion to the quantity of declivity in their bed: […] .”

   “[…]whoever takes the trouble of observing how the water runs longitudinally in the ruts on a convex road, although the declivity down the sides be incomparably greater than in the direction which it is compelled to take in the ruts, will soon see the propriety of constructing roads so as to have the water rim length-ways upon them, instead of attempting to gain a declivity, by making it run from the middle to the sides.”

   “[…]a line was measured down the hill on the right of 420, and the angle of declivity is 23°, which shortens the line 33 links;[…].”

   “A rocky cliff appeared, mounds of turned–up earth by the shore, houses on a hill, others with iron roofs, amongst a waste of excavations, or hanging to the declivity.”

2. A downward bend in a path.
3. 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.

   “1979, Entomology Circular, Issue 200, Part 366, Division of Plant Industry, page number not shown, Males of all species have more developed armature of the elytral declivity than females (Figs. S, 6, 8, 9, 11-14).”

   “Propodeum in profile with upper lobe of declivity elongate and narrow, subspiniform, almost as long as lower lobe.”