: lighthearted unconcern : nonchalance
Observe the very thin line between indifference, apathy, (the recent) stolidness and nonchalance, coolness, INSOUCIANCE. The key concept in this gap is "lightheartedness"—the vast canyon between not caring and not having a care in the world. There is something inherently romantic in the latter three traits, as though everything just rolls off one's back.
The word INSOUCIANCE creates some discrepancies, though. In the thesaurus, INSOUCIANCE is paired with aloofness, disregard, emotionlessness, lethargy. On the other hand, the adjective form INSOUCIANT turns up carefree, happy-go-lucky, lighthearted, and nonchalant. Interesting. I want to pretend this means something, but it probably does not.
INSOUCIANCE comes from the french verb soucier, to trouble or disturb. So: not bothered. Couldn't care less.
I suppose INSOUCIANCE or nonchalance then implies a carefree indifference, while apathy implies a jaded indifference.
I think I will now put this to bed.