Levity in behaviour or manner; fickleness, inconstancy, frivolity; thoughtlessness, carelessness, indifference; lack of seriousness.

As a moral or mental quality, in various senses. Want of serious thought or reflexion; frivolity. Also (now chiefly), ‘Trifling gaiety’ (Johnson)…

The quality or condition of being gay; cheerfulness, mirth.

The quality of being shallow. Want of depth of character, thought, knowledge, etc.; superficiality.

The state or quality of being ludicrous.

The quality or state of being flighty; giddy capriciousness, fickleness or whimsicalness.

trivial-minded adj. (whence trivial-mindedness).