The term 'prime MOVER' is used to describe a person or thing that is the main source of power or motivation for an action. The crossword solutions for this term are MOVER (5 letters), MASTERMIND (10 letters), AUTHOR (6 letters), ENGINE (6 letters), and MACHINE (7 letters). A MOVER is someone who moves things from one place to another, a MASTERMIND is someone who is the leader or originator of a plan, an AUTHOR is someone who creates written works, an ENGINE is a device that converts energy into motion, and a MACHINE is a device that performs a specific task. All of these words can be used to describe a prime MOVER, as they all refer to a person or thing that is the main source of power or motivation for an action.