proclivity (n.)

"inclination, propensity, tendency," 1590s, from French proclivité or directly from Latin proclivitatem (nominative proclivitas) "a tendency, predisposition, propensity," from proclivis "prone to," literally "sloping, inclined," from pro "forward" (see pro-) + clivus "a slope" (from PIE *klei-wo-, suffixed form of root *klei- "to lean").

Proclivous (1730) "tending, sloping" seems to have been a mere dictionary word for most of its existence, though it began to acquire some technical senses after c. 1890.

updated on November 23, 2020