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Insouciant
Emotional Tone
Insouciant carries a light-hearted, easygoing emotional tone, often suggesting a positive, free-spirited mindset. 
Not Always Positive
In some situations, 'insouciant' can have a negative implication, suggesting irresponsibility or lack of proper concern. 
Literary Flair
The word has a somewhat literary feel and may be used to inject a bit of stylishness into the language. 