impetus

I noun actuation, boost, call, drive, encouragement, energy, force, goad, impellent, impelling force, impulse, impulsion, incentive, influence, instigation, jog, jolt, kick, momentum, motive, moving force, pressure, propellant, propulsion, propulsive force, purpose, push, reason, shove, spur, start, stimulus, thrust, urge, vis II index assault III index boom (prosperity), catalyst, determinant IV index force (strength), impulse V index incentive, instigation, reason (basis), stimulus