Motive (noun)

1. A reason or intention behind an action or decision.
2. A force or influence that stimulates action or determines behavior.

Origin:

Late middle english (in the sense "driving force"): from latin motivus, from movere "to move".

Examples:

1. The police are trying to find the motive behind the murder.
2. Her motive for quitting her job was to start her own business.
3. Money is not his only motive for working.
4. The company is investigating the motive for the cyberattack.
5. The motive for the theft is still unknown.