v.
1 tremble, quiver, shake, shiver, vibrate, waver, shudder, fluctuate, oscillate, flutter:
His voice quavered with emotion as he described his rescue.
n.
2 trembling, tremble, quiver, quivering, tremor, shaking, vibration, wavering, break, fluctuation, oscillation:
Only a slight quaver in her voice betrayed her feeling of panic.