ETYM Old Fren. action, Latin actio, from agere to do. Related to Act.
1. Something done (usually as opposed to something said).
2. An act by a government body or supranational organization.
3. The operating part that transmits power to a mechanism.
4. The series of events that form a plot.
5. The state of being active; SYN. activity, activeness.
6. The trait of being active and energetic and forceful.
7. The most important or interesting work or activity in a specific area or field

In music, the internal mechanism of a keyboard instrument, such as the piano, harpsichord, or organ, which links the keys to the strings or pipes when the keys are depressed. On a string instrument, it refers to the space between the strings and the fingerboard.

In law, one of the proceedings whereby a person or agency seeks to enforce rights in a civil court.
Actions fall into three principal categories, namely civil (such as the enforcement of a debt), criminal (in which a government agency prosecutes a defendant accused of violation of a criminal law), and penal (violation of a law enacted to preserve public order).

1. Institute legal proceedings against; file a suit against
2. Put in effect