Nonchalance (noun)

The state or quality of being nonchalant; casualness; indifference.

Origin:

French nonchalance, from nonchalant, present participle of nonchaloir to be cool, from non- + chaloir to be warm, from latin calēre to be warm.

Examples:

1. He approached the situation with nonchalance and took it in his stride.
2. Her nonchalance made it hard to tell if she was really interested in the conversation.
3. He spoke with nonchalance, which made him seem uninterested in the subject.
4. The actress played the part with nonchalance, making the audience believe that it was natural for her.
5. His nonchalance made it hard to know if he was serious or joking.