A pushbutton switch with a return spring is called a(n) __________ switch.

A pushbutton switch with a return spring is known as a momentary switch because it is designed to only remain engaged while being pressed. When the button is released, the return spring automatically brings it back to its original position, interrupting the circuit and effectively turning off the switched device. This characteristic allows momentary switches to be used in applications where temporary activation is required, such as door bells, manual input controls, and various control panels. The term "momentary" accurately describes the function of the switch, which only remains closed during the period it is actively pressed.