noun

1. A person or thing that is acting or capable of acting.

2. Any component that is not passive. See Passivity (engineering).

adjective

1. Having the power or quality of acting; causing change; communicating action or motion; acting;—opposed to passive, that receives.

   “certain active principles”

2. Quick in physical movement; of an agile and vigorous body; nimble.

   “an active child or animal”

3. In action; actually proceeding; working; in force

   “active hostilities”

Synonyms: acting, agile, nimble, busy, deedful, diligent, energetic, in action