Meaning

1. The state or quality of being active; activeness.
2. Something done as an action or a movement.
3. Something done for pleasure or entertainment, especially one involving movement or an excursion.
4. The lexical aspect (aktionsart) of verbs or predicates that change over time and have no natural end point.
5. The number of radioactive decays per unit time. Unit for it: becquerel or curie
6. The property of substances to react with other substances