Coolheaded (adjective)

Not easily excited or flustered; calm and level-headed.

Origin:

From the phrase "cool head".

Examples:

1. The coolheaded pilot was able to land the plane safely during the emergency.
2. She remained coolheaded even when the situation seemed to be out of control.
3. He was the most coolheaded person I had ever met.
4. The coolheaded detective was able to solve the case.
5. The coolheaded negotiator was able to bring the two sides to an agreement.