blithe
BLYTHEadjMeaning cheerful and carefree, sometimes carelessly so
Memory hook BLITHE = BLISS + LIGHT. Pip skips home whistling, blissful and light as a feather, without a care in the world, not even for the storm cloud right behind him. He is blithe.
Humming a blithe tune, Zoe skipped down the lane to the pond.
In context His blithe attitude toward deadlines worried his teammates; he whistled and joked while the project sat unfinished the night before it was due.
Similar carefree, lighthearted, breezy, unconcerned
Opposite worried, anxious, careful
From Old English blithe, “joyful,” related to bliss.