fear, fearfulness, fright - an emotion experienced in anticipation of some specific pain or danger (usually accompanied by a desire to flee or fight)

motion - a state of change; "they were in a state of steady motion"

tremolo - (music) a tremulous effect produced by rapid repetition of a single tone or rapid alternation of two tones

tremor - shaking or trembling (usually resulting from weakness or stress or disease)

case - a portable container for carrying several objects; "the musicians left their instrument cases backstage"

movement, motility, motion, move - a change of position that does not entail a change of location; "the reflex motion of his eyebrows revealed his surprise"; "movement is a sign of life"; "an impatient move of his hand"; "gastrointestinal motility"

tremor, shudder - an involuntary vibration (as if from illness or fear)

tremble - move or jerk quickly and involuntarily up and down or sideways; "His hands were trembling when he signed the document"

move back and forth - move in one direction and then into the opposite direction

move - move so as to change position, perform a nontranslational motion; "He moved his hand slightly to the right"

pulsate, pulse, throb - expand and contract rhythmically; beat rhythmically; "The baby's heart was pulsating again after the surgeon massaged it"