The term 'MOTOR'S POWER, INFORMALLY' can be solved by the crossword solution 'HORSES, ' which is a six-letter word. This term is referring to the power of an engine, usually measured in horsepower. Horsepower is a unit of measurement that was originally derived from the amount of power a horse could generate. It is still used today to measure the power of engines, such as those found in cars and other motorized vehicles.