1. Someone who acts or has the power or authority to act: A revenuer is a government agent whose duty it is to collect revenue.
2. Anyone empowered to act for or to represent another person; An agent can be an author's agent or an insurance agent.
3. A means by which something is done or that is caused to be done; an instrument: The building of a daycare center for little children proved to be an agent of definite improvement in the community.
4. A force or substance that causes a change: Examples of an agent can be a chemical agent or an infectious agent.

June put a bleaching agent into the white load of laundry to be washed.
5. A representative or official of a government or administrative department of a government: Jack's uncle was an agent for the FBI.
6. A spy: In the movie, the man with the black coat and hat turned out to be an undercover agent!
7. In linguistics, the noun or noun phrase that specifies the person through whom or the means by which an action is effected: An agent can be the person who does something, like the girl (the agent) started making the cookies for Christmas early in December!

1. A person who is employed to encourage people to break the law so they can be arrested and prosecuted: The government used agents provocateurs to try to undermine the opposition party so they would lose the election.
2. A secret agent implanted in an organization; such as, a trade union or political party, to incite its members to actions or declarations that will result in penalties or punishment for them: In the story that Jim was reading, the secret service decided to ask a young woman to be an agent provocateur in order to provoke a suspected person to perform an illegal deed which would then result in his conviction.

A synthetic or natural drug that stimulates beta or sympathetic receptors.

A substance that interferes with the transmission of stimuli through pathways that normally allow sympathetic nervous inhibiting stimuli to be effective.

These agents are used in treating hypertension, angina, certain cardiac arrhythmias, and postmyocardial infarction.

They may also be helpful in preventing migraine and in treating stage fright and benign essential tremor.

A drug that blocks the stimulation of cells by histamine.

This type of agent acts by interfering with the action of histamine rather than by preventing its secretion.

Any of various synthetic drugs which lower the blood glucose level and are used to treat type 2 diabetes mellitus.

Such drugs may stimulate the synthesis of insulin by the pancreatic beta cells, inhibit glucose production, facilitate the transportation of glucose to muscle cells, and sometimes increase the number of receptor sites where insulin can be bound and can imitate the process of breaking down glucose.

Someone who tries to get secret information about another country, government, etc.: Mildred's sister was accused of being a secret agent for a foreign government.