from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun An extremely precise timekeeping device regulated in correspondence with a characteristic invariant frequency of an atomic or molecular system.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun An extremely accurate reference clock whose operation is based on an atomic process, typically the frequency of electromagnetic radiation associated with a specified energy-level transition in an element such as cesium.
  • noun proscribed A radio clock.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun a timepiece that derives its time scale from the vibration of atoms or molecules


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  • A type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, and to control the frequency of television broadcasts and GPS satellite signals. (Wikipedia)

    May 29, 2008