Final answer:
The principal member of the grid supporting a suspended ceiling system is known as the Main runner. It is a sheet-metal channel or tee suspended from the overhead structure by hanger wires and provides the framework for ceiling tiles or panels.
Step-by-step explanation:
The principal member of the grid supporting a suspended ceiling system is typically known as the Main runner. These are usually sheet-metal channels or tees that are suspended from the overhead structure by hanger wires. They are crucial in providing the framework to which the ceiling tiles or panels are attached. In classical architecture, elements such as the entablature play a supporting role, similar to main runners, but in a much more decorative and structural context, including components like the cornice, frieze, and architrave.
However, for the practical purposes of a modern suspended ceiling system, the main runner is the central part responsible for the overall support and integrity of the ceiling grid.