The term 'motor add-on' refers to an accessory or attachment that can be added to a motor vehicle. The two crossword solutions for this term are OLA (3 letters) and CADE (4 letters). OLA stands for On-Line Accelerator, which is a device that increases the power of a motor vehicle's engine. CADE stands for Cruise Adaptive Drive, which is a system that helps a vehicle maintain a steady speed on a highway.