behaviour that shows a lack of respect for something serious and that treats it with humour (Oxford)
humour or lack of seriousness, especially during a serious occasion (Cambridge)
The joke provided a moment of levity in an otherwise dreary meeting. (Oxford)
A brief moment of levity amid the solemn proceedings. (Cambridge)
moment of levity
brief moment of levity amid the solemn proceedings
Frivolity
Absurdity
Seriousness
Sense
Levity