OPOSSUMS ARE MARSUPIALS. If you open just about any field guide to North American mammals, the opossum will probably be the very first of the 380 or so mammal species described. That's because opossums are our only marsupial, and marsupials are considered very ancient forms of mammals.
operator - an agent that operates some apparatus or machine; the operator of the switchboard. manipulator. causal agency, causal agent, cause - any entity that produces an effect or is responsible for events or results. company operator - an operator who works for a company. driver - the operator of a motor vehicle.
operation. n. 1. the act, process, or manner of operating. 2. the state of being in effect, in action, or operative (esp in the phrases in or into operation). 3. a process, method, or series of acts, esp of a practical or mechanical nature.