What do you call the cover of the engine compartment in a vehicle?

The cover of the engine compartment in a vehicle is referred to as the bonnet. This term is commonly used in British English to describe the hinged cover that rests over the engine and allows access for maintenance and repairs. In automotive terminology, the bonnet serves not only to provide access but also to protect engine components from dirt and debris, and it contributes to the vehicle's overall aerodynamics and aesthetics.

The other terms listed refer to different components of a vehicle: the deck lid refers to the rear cover of a vehicle (often associated with the trunk), a spoiler is an aerodynamic feature designed to improve stability and reduce drag, and a fender is the part of the vehicle body that surrounds the wheel well. Therefore, the correct association of "bonnet" with the engine compartment cover is what makes this option the right choice.