The term 'motor monitor' refers to a device that measures the speed of a motor. The crossword solution for this term is 'TACH, ' which is an abbreviation for tachometer, a device used to measure the rotational speed of a motor. Tachometers are often used in automotive applications, such as measuring the revolutions per minute (RPM) of an engine. They can also be used to measure the speed of other types of motors, such as those used in industrial machinery.