1) Buoyancy 2) Feeling 3) Flippancy 4) Flippant talk 5) Frivolous quality 6) Funny business 7) Humor 8) Imponderability 9) Inappropriate frivolity 10) Lack of gravitas 11) Lightness 12) Mirth 13) Volatility 1) Flippancy 2) Frivolity 3) Humorousness 4) Jocoseness 5) Merriness 6) Playfulness 
[Soundtrack] This category is for concept cars that may have been shown in car shows or appeared in the media, and will not enter into production or have not yet. They may or may not be planned for further development, with possible intent to enter production at a future date, in a next generation of vehicles from an automobile manufacturer...
• (n.) Lack of gravity and earnestness in deportment or character; trifling gayety; frivolity; sportiveness; vanity. • (n.) The quality of weighing less than something else of equal bulk; relative lightness, especially as shown by rising through, or floating upon, a contiguous substance; buoyancy; -- opposed to gravity. • (n.) Lack o...
Lev'i·ty (lĕv'ĭ*tȳ) noun [ Latin levitas , from levis light in weight; akin to levare to raise. See Lever , noun ] 1. The quality of weighing less than something else of equal bulk; relative lightness, especially as show...
lack of seriousness 
[n] - feeling an inappropriate lack of seriousness 2. [n] - lightness of manner
[Wuthering Heights] lack of seriousness.
noun a manner lacking seriousness
[SAT terms] a manner lacking seriousness a manner lacking seriousness[Intelligent words] a manner lacking seriousness