noun, plural ac·cliv·i·ties.
- an upward slope, as of ground; an ascent (opposed to declivity).
noun plural -ties
- an upward slope, esp of the groundCompare declivity
1610s, from Latin acclivitatem (nominative acclivitas) “an ascending direction, an upward steepness,” from acclivis “mounting upwards, ascending,” from ad- “up” (see ad-) + clivus “hill, a slope,” from PIE *klei-wo-, suffixed form of *klei- “to lean” (see lean (v.)).