impetus

 
Pronunciation: /ˈɪmpɪtəs/

noun

[mass noun]
  • the force or energy with which a body moves: hit the booster coil before the flywheel loses all its impetus
  • something that makes a process or activity happen or happen more quickly: the ending of the Cold War gave new impetus to idealism

Origin:

mid 17th century: from Latin, 'assault, force', from impetere 'assail', from in- 'towards' + petere 'seek'