Definition of "actor"

(obsolete, law) Someone who institutes a legal suit; a plaintiff or complainant.

(obsolete) Someone acting on behalf of someone else; a guardian.

Someone or something that takes part in some action; a doer, an agent.  quotations  examples

A person who acts a part in a theatrical play or (later) in film or television; a dramatic performer.  quotations  examples

(obsolete, Ancient Rome) An advocate or proctor in civil courts or causes.

(grammar) The subject performing the action of a verb.  examples

(software engineering) The entity that performs a role (in use case analysis).  examples