Entry 1 sense Webster, 1913 Insouciance /ĭnˌ-so͞os'-ē-əns/ · In·sou·ciance · IPA /ɪnˈsuːsi.əns/ 01 n. Carelessness; heedlessness; thoughtlessness; unconcern. 1. Carelessness; heedlessness; thoughtlessness; unconcern.