tremor

(trĕmˈər)

1. A shaking or vibrating movement, as of the earth.
2. A trembling or quivering effect: a tremor of aspen leaves.
3. An involuntary trembling or quivering, as from nervous agitation or weakness.
4. A nervous quiver or thrill: felt a tremor of joy.
5. A state or feeling of nervous agitation or tension.
6. A tremulous sound; a quaver.