Merriam-Webster Collegiate Dictionary - agency

 noun  (plural -cies)  Date: 1640  1.  a. the office or function of an agent  b. the relationship between a principal and that person's agent  2. the capacity, condition, or state of acting or of exerting power ; operation  3. a person or thing through which power is exerted or an end is achieved ; instrumentality communicated through the ~ of the ambassador  4. an establishment engaged in doing business for another an advertising ~  5. an administrative division (as of a government) the ~ for consumer protection