tremble

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To shake involuntarily, as from excitement or anger; quake. synonym: shake.
• intransitive verb To feel fear or anxiety.
• intransitive verb To vibrate or quiver.
• noun The act or state of trembling.
• noun A convulsive fit of shaking. Used with the.
• noun Poisoning of domestic animals, especially cattle and sheep, caused by eating white snakeroot or the composite plant Isocoma pluriflora of the southwest United States and northern Mexico, and characterized by muscular tremors and weakening.
• noun Any of several other animal diseases characterized by trembling, such as louping ill.

from The Century Dictionary.

• noun The act or state of trembling; an involuntary quivering or shivering as from cold or fear.
• noun plural A form of disease or diseased condition in man or animals, characterized by continued trembling or tremulousness; specifically, in some parts of the United States, a disease of domestic animals, under peculiar local conditions, affecting the quality of the milk and flesh, and known as milk-sickness when communicated through these to human beings. See milk-sickness.
• To be affected with slight, quick, and continued vibratory movements; be moved in a quivering manner by some external force.
• To be affected with involuntary muscular agitation; be agitated convulsively from either a physical or a moral cause; be in a tremor; quake; shake: as, to tremble with fatigue; his hand trembled from excitement.
• To feel or manifest a quivering agitation; be tremulous or shaky; quiver; quaver: as, his voice trembled from emotion.
• Figuratively, to be in doubt or suspense; oscillate between certainty and uncertainty; hang upon chance.

from the GNU version of the Collaborative International Dictionary of English.

• noun An involuntary shaking or quivering.
• intransitive verb To shake involuntarily, as with fear, cold, or weakness; to quake; to quiver; to shiver; to shudder; -- said of a person or an animal.
• intransitive verb To totter; to shake; -- said of a thing.
• intransitive verb To quaver or shake, as sound; to be tremulous; as the voice trembles.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To shake, quiver, or vibrate.
• noun A shake, quiver, or vibration.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a reflex motion caused by cold or fear or excitement
• verb move or jerk quickly and involuntarily up and down or sideways