levity (n.)

1560s, "want of seriousness, frivolity," from French levite, from Latin levitatem (nominative levitas) "lightness," literal and figurative; "light-mindedness, frivolity," from levis "light" in weight, from PIE root *legwh- "not heavy, having little weight." In old science (16c.-17c.), the name of a force or property of physical bodies, the opposite of gravity, causing them to tend to rise.