1. Shake, quiver, tremble, vibrate refer to an agitated movement that, in living things, is often involuntary. To shake is to agitate more or less quickly, abruptly, and often unevenly so as to disturb the poise, stability, or equilibrium of a person or thing: a pole shaking under his weight. To quiver is to exhibit a slight vibratory motion such as that resulting from disturbed or irregular (surface) tension: The surface of the pool quivered in the breeze. To tremble (used more often of a person) is to be agitated by intermittent, involuntary movements of the muscles, much like shivering and caused by fear, cold, weakness, great emotion, etc.: Even stout hearts tremble with dismay. To vibrate is to exhibit a rapid, rhythmical motion: A violin string vibrates when a bow is drawn across it.

Did you mean unshakable?