1. An involuntary vibration; as if from an illness or from suden fear.
2. Shaking or trembling; usually resulting from weakness, stress, or disease.
3. A sudden and usually brief feeling of excitement, nervousness, or anticipation: "Tremor or shaking movements in a person's body; usually, because of fright, excitement, or an illness."
4. A small seismic activity; such as, a minimal earthquake: "Tremors from an earthquake may have sudden and violent movements coming from the earth's surface."

The uncontrollable shaking (tremor) of the hands and head and sometimes other parts of the body: "Essential tremor is considered to be the most common of all bodily movement disorders and it is estimated to affect three to four million people in the United States."