Impetus
Part of speech: noun
Definition: Something that impels, a stimulating factor. A force, either internal or external, that impels; an impulse. The force or energy associated with a moving body; a stimulus. An activity in response to a stimulus.
Example sentence: Sometimes nationalism can be jingoistic - even fascistic - but it can also be a constructive impetus that helps to unify a nation. Those whose nationalist critique of parties finds resonance with masses of voters can acquire vast power. We can only hope that they know what to do with it.
Impulsion
Part of speech: noun
Definition: The act of impelling or driving onward, or the state of being impelled; the sudden or momentary agency of a body in motion on another body; also, the impelling force, or impulse.Influence acting unexpectedly or temporarily on the mind; sudden motive or influence; impulse.