in ‧ sou ‧ ci ‧ ance /ɪnˈsuːsiəns/ BrE AmE noun [uncountable] formal
[ Date: 1800-1900 ; Language: French ; Origin: soucier 'to trouble' ]
a cheerful feeling of not caring or worrying about anything SYN nonchalance :
an air of insouciance
—insouciant adjective
—insouciantly adverb