IPA: /ˌɪnˈsuːsiənt/
KK: /ɪnˈsuːsiənt/
Showing a relaxed and carefree attitude, not worried about anything.
Despite the chaos around her, she remained insouciant and calm.
Insouciant is derived from the French word 'insouciant', which comes from 'in-' (meaning not) and 'souci' (meaning worry or concern). The word describes a state of being carefree or unconcerned, literally meaning not worried.
Think of someone who is 'not' ('in-') 'worried' ('souci') about anything — that's why insouciant means carefree.