Nonchalant means casually unbothered. A shrug where other people would panic.
The word usually carries a hint that the calm is being performed, since somebody nonchalant is often working quite hard at looking as though they are not. That makes it useful in fiction, where a nonchalant air and a nonchalant shrug are standard. It came from French and kept the spelling, which is why the ch is pronounced like sh. The adverb nonchalantly is commoner than the adjective, and the noun is nonchalance.
1adjectivenonchalantCalm and casual, showing no anxiety or interest.
“He was maddeningly nonchalant about the whole thing.”
synonyms: unconcerned, offhand
Old French
nonchaloir — to be unconcerned
French
nonchalant
English, today
nonchalant
French nonchalant, from Old French nonchaloir (“to be unconcerned”), from non- + chaloir, from Latin - non + calēre.
Etymology from Wiktionary, CC BY-SA