blithe
Cheerful and carefree, not worried about problems.
Blithe means carefree and lighthearted, without worry or concern. Someone with a blithe attitude moves through life cheerfully, not weighed down by anxieties or troubles. You might see a blithe expression on someone's face as they walk through a sunny park, humming a tune without a care in the world.
The word often describes a pleasant kind of cheerfulness: a blithe spirit enjoys the moment rather than fretting about what might go wrong. A character in a story might have a blithe personality, always optimistic and easygoing even when challenges arise.
However, blithe can also suggest being unconcerned when you should be paying attention. If someone shows blithe disregard for the rules, they're ignoring them carelessly, as if rules don't matter. A student who skips homework with blithe indifference isn't admirably carefree but rather irresponsible and unconcerned about the consequences.
The related word blithely works as an adverb: someone might blithely ignore warnings or blithely walk into a situation without thinking it through. Context matters: being blithe about a beautiful day is delightful, but being blithe about your responsibilities usually leads to trouble.