unworried
Calm and not worried or anxious about something.
Unworried means feeling calm and free from concern or anxiety. When you're unworried about tomorrow's spelling test, you're not nervous or stressed because you've studied and feel prepared. An unworried mind is peaceful and relaxed, not tangled up with “what ifs” and fears.
You might notice someone is unworried by how they act: they smile easily, sleep soundly, and don't constantly check or fret about things. A student who's unworried about making the team just does their best at tryouts without the jitters. A parent might seem unworried when their child goes to camp, trusting that everything will work out.
Being unworried doesn't mean being careless or irresponsible. Someone can take things seriously and still feel unworried because they've done what they can and trust the outcome. A well-prepared camper can head into the woods feeling unworried because their gear is packed, their skills are solid, and they're ready for adventure. The word captures that particular kind of calm that comes when you've either handled what needs handling or decided that something isn't worth your worry in the first place.