proclivity (n.) Look up proclivity at Dictionary.com
1590s, from Middle 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" (see lean (v.)).