Agent noun ˈā-jənt
: a person who does business for another person : a person who acts on behalf of another

: a person who tries to get secret information about another country, government, etc. : a person or thing that causes something to happen
1
: something that produces or is capable of producing an effect
2
: a chemically, physically, or biologically active principle

a : something that produces or is capable of producing an effect : an active or efficient cause.
3
: a means or instrument by which a guiding intelligence achieves a result
4
: one who is authorized to act for or in the place of another: as
a : a representative, emissary, or official of a government <crown agent> <federal agent>
b : one engaged in undercover activities (as espionage) : spy <secret agent>

c : a business representative (as of an athlete or entertainer) whose expressions are designed to send forth subliminal messages which are intended to influence one’s mindset <a theatrical agent>.
5

A computer application designed to automate certain tasks (as gathering information online)