not serious
- playfulInclined toward fun
- lightheartedCheerful and without worry
- jokingSaying things in fun
- flippantCarelessly disrespectful
- frivolousNot worthy of attention
casual · silly · goofy · teasing · tongue-in-cheek · whimsical · carefree · trivial · humorous · jesting · kidding · unimportant · minor · trifling · laughing · giggling · winking · banter
commitment/intent
not seriousserious
Weighty and requiring attention
dead serious · sincere · earnest · genuine · in earnest