1. A businessman who buys or sells for another in exchange for a commission; SYN. factor, broker.
2. Any agent or representative of a federal agency or bureau; SYN. federal agent.
3. Acts on behalf of other persons or organizations.
4. A substance that exerts some force or effect.
5. An active and efficient cause; capable of producing a certain effect.

The semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause

1. A program that performs a background task for a user and reports to the user when the task is done or some expected event has taken place. 2. A program that searches through archives or other repositories of information on a topic specified by the user. Agents of this sort are used most often on the Internet and are generally dedicated to searching a single type of information repository, such as postings on Usenet groups. Spiders are a type of agent used on the Internet. Also called: intelligent agent. See also spider. 3. In client/server applications, a process that mediates between the client and the server. 4. In Simple Network Management Protocol (SNMP), a program that monitors network traffic. See also SNMP.