DE- n.
A prefix from Latin de down, from, away; as in debark, decline, decease, deduct, decamp. In words from the French it is equivalent to Latin dis- apart, away; or sometimes to de. Cf. Dis-. It is negative and opposite in derange, deform, destroy, etc. It is intensive in deprave, despoil, declare, desolate, etc.…
DECLINE v. 2 definitions
To bend, or lean downward; to take a downward direction; to bend over or hang down, as from weakness, weariness, despondency, etc.; to condescend. "With declining head." Shak. He . . . would decline even to the lowest of his family. Lady Hutchinson. Disdaining to decline, Slowly he falls, amidst triumphant cries. Byron…
DECLIVITY n.
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.