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{system, computer, user}
{math, energy, light}
{day, year, event}
{church, century, christian}
{@card@, make, design}
{language, word, form}
{theory, work, human}
{island, water, area}
{ship, engine, design}
{town, population, incorporate}

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately (via Dutch, Northern French, and Medieval Latin) from the Celtic words clagan and clocca meaning "bell". A silent instrument lacking such a mechanism has traditionally been known as a timepiece.[1] In general usage today a "clock" refers to any device for measuring and displaying the time. Watches and other timepieces that can be carried on one's person are often distinguished from clocks.[2]

The clock is one of the oldest human inventions, meeting the need to consistently measure intervals of time shorter than the natural units: the day; the lunar month; and the year. Devices operating on several different physical processes have been used over the millennia, culminating in the clocks of today.


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