Mission (noun)

1. An important task or duty that has been assigned to someone.
2. an official group of people sent to a foreign country to do a particular job.

Origin:

Middle english: from old french, from latin missio(n-), from mittere "to send".

Examples:

1. He was on a mission.
2. She was on a mission to help the poor.
3. They were on a mission to explore the galaxy.
4. He was on a mission to find his family.
5. She was on a mission to save the planet.