Function (noun)

1. The purpose for which something is designed or exists.
2. A particular activity or task that is assigned to someone.

Origin:

Late middle english: from latin functio(n-), from fungi "perform".

Examples:

1. The function of the machine was to process data.
2. The function of the government is to serve the people.
3. She was asked to perform the function of lead singer for the band.
4. The function of the muscle is to contract and produce movement.
5. The function of the meeting was to discuss and make decisions on important company matters.