Finding a Synonym for 'Insouciant'

Choose the word that is most similar in meaning to the word 'insouciant'.

The term 'insouciant' describes an attitude of carelessness or indifference, often implying a lighthearted, unconcerned demeanor. It is usually used to characterize a person who is unconcerned about the future or the consequences of their actions. Your task is to select the word that best captures this meaning.