nonchalant
non-shuh-LAHNTadjMeaning casually unconcerned, as if nothing much matters
Memory hook NON-CHALANT: “I shall NOT care.”. Everyone is hunting for the lost keys, but the cat just yawns in the sunny window: “I shall not care.” The cat is nonchalant.
With a nonchalant shrug, Dev said he had probably won the contest.
In context The rest of the family was frantic about the lost keys, but the cat was nonchalant, yawning and stretching in the sunny window as if nothing had happened.
Similar casual, unconcerned, offhand, blasé
Opposite anxious, concerned, worried
From French nonchalant, “not caring”: non (not) + chaloir (to concern), from Latin calere, “to be warm.”