Nonchalant (adjective)

1. Appearing or feeling relaxed and calm, especially in a difficult situation.
2. Not showing concern, interest, or enthusiasm.

Origin:

The word "nonchalant" comes from french, and it is derived from "non" meaning "not" and "chalan" meaning "vigorous" or "careful". it was first used in english in the late 18th century.

Examples:

1. Despite the chaos around him, the pilot remained nonchalant, guiding the plane to a safe landing.
2. She was nonchalant about the whole ordeal, as if it was just another day in the office.
3. He gave a nonchalant shrug when asked about his plans for the weekend.
4. She tried to be nonchalant about her feelings, but her voice betrayed her.
5. The thief was nonchalant as they walked out of the store with the stolen goods.