WordNet sense 1 (a theme that is elaborated on in a piece of music):

motif

WordNet sense 2 (causing or able to cause motion):

motor

WordNet sense 3 (impelling to action):

motivating, motivative

WordNet sense 4 (producing an effect):

causative

WordNet sense 5 (the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior):

motivation, need