noun
: a precision clock that depends for its operation on an electrical oscillator (as a quartz crystal) regulated by the natural vibration frequencies of an atomic system (as a beam of cesium atoms or of ammonia molecules)
noun
: a precision clock that depends for its operation on an electrical oscillator (as a quartz crystal) regulated by the natural vibration frequencies of an atomic system (as a beam of cesium atoms or of ammonia molecules)
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012