IPA: /ˌɪnˈsuːsiˌɑːns/
KK: /ɪnˈsuːsiˌɑːns/
A carefree attitude or a state of being unconcerned about things that might worry others.
Her insouciance in the face of danger surprised everyone around her.
Insouciance is derived from the French word 'insouciance', which is formed from the prefix 'in-' (meaning not) and 'souci' (meaning worry or concern). The word describes a state of being carefree or unconcerned, indicating a lack of worry.
Think of 'not' ('in-') worrying ('souci') to remember that insouciance means a carefree attitude.