undulate

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. the door suddenly swung open sway implies a slow swinging or teetering movement. trees swaying in the breeze oscillate stresses a usually regular alternation of direction. an oscillating fan vibrate suggests the rapid oscillation of an elastic body under stress or impact. the vibrating strings of a piano fluctuate suggests constant irregular changes of level, intensity, or value. fluctuating interest rates waver stresses irregular motion suggestive of reeling or tottering. the exhausted runner wavered before collapsing undulate suggests a gentle wavelike motion. an undulating sea of grass