/ ɪnˈsuːsiəns; NAmE / noun
[ U ] ( formal ) the state of not being worried about anything
SYN nonchalance :
She hid her worries behind an air of insouciance.
► in·sou·ci·ant / -siənt; NAmE / adjective
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WORD ORIGIN
late 18th cent.: French , from insouciant , from in- not + souciant worrying (present participle of soucier ).