swing, sway, oscillate, vibrate, fluctuate, waver, undulate mean to move from one direction to its opposite.

swing implies a movement of something attached at one end or one side.

sway implies a slow swinging or teetering movement.

oscillate stresses a usually regular alternation of direction.

vibrate suggests the rapid oscillation of an elastic body under stress or impact.

fluctuate suggests constant irregular changes of level, intensity, or value.

waver stresses irregular motion suggestive of reeling or tottering.

undulate suggests a gentle wavelike motion.

hesitate, waver, vacillate, falter mean to show irresolution or uncertainty.

hesitate implies a pause before deciding or acting or choosing.

waver implies hesitation after seeming to decide and so connotes weakness or a retreat.

vacillate implies prolonged hesitation from inability to reach a firm decision.

falter implies a wavering or stumbling and often connotes nervousness, lack of courage, or outright fear.