Definitions
1.nounA person who performs, plays a part in a theatrical play or film.
2.nounOne who acts; a doer.
3.nounOne who takes part in a situation.
4.nounAn advocate or proctor in civil courts or causes.
5.nounOne who institutes a suit; plaintiff or complainant.
6.noun(policy debate) One who enacts a certain policy action.
7.nounThe entity that performs a role (in use case analysis).
8.noun(grammar) The most agent-like argument of a clause, e.g. 'the torpedo' in "The torpedo sank the boat" and "The torpedo fired".