Earth·quake n. A shaking, trembling, or concussion of the earth, due to subterranean causes, often accompanied by a rumbling noise. The wave of shock sometimes traverses half a hemisphere, destroying cities and many thousand lives; -- called also earthdin, earthquave, and earthshock.
 Earthquake alarm, a bell signal constructed to operate on the theory that a few seconds before the occurrence of an earthquake the magnet temporarily loses its power.