The term 'shaky motion' can be summarized as a TREMOR, which is a 6 letter word. A TREMOR is an involuntary, rhythmic muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is a common neurological disorder that most often affects the hands and arms, but can also affect the head, vocal cords, torso, and legs. Tremors can be caused by a variety of medical conditions, including Parkinson's disease, multiple sclerosis, and essential TREMOR.