Learner's definition of AGENT
1 : a person who does business for another person : a person who acts on behalf of another
They worked with a travel agent to plan their vacation.
The actor got a starring role through his (theatrical) agent.
a literary agent [=a person who helps writers to get their works published]
2 : a person who tries to get secret information about another country, government, etc. : spy secret agent 3 : a person or thing that causes something to happen 4 : something (such as a chemical) that is used to produce a particular effect or result
The drug is an effective agent for the treatment of asthma.
the main flavoring agent in the drink
Cornstarch is used as a thickening agent in sauces.