nonchalant

marked by blithe unconcern

Indifferent; careless; cool.

French, from non + chaleureux

“Pericles had retreated. "Ce nonchalant" was not quite true to his title, when he heard that Emilia had flown.”

— George Meredith, Complete Project Gutenberg Works of George Meredith

“Some of the prisoners were reportedly despondent, but others were nonchalant, even smoking tobacco.”