proxy

noun | \ ˈpräk-sē \

1. : the act or practice of a person serving as an authorized agent or substitute for another —used especially in the phrase by proxy

2. a : authority or power to act for another

   b : something serving to replace or substitute for another thing

3. a : a person authorized to act or make decisions for another appointed a health-care proxy

   b : something serving to replace or substitute for another thing