Real Dictionary

clock in American English 1
a device used for measuring and indicating time, usually by means of pointers moving over a dial: clocks, unlike watches, are not meant to be worn or carried about
to measure the speed or record the time of (a race, runner, motorist, etc.) with a stopwatch or other timing device
noun: an instrument for measuring and recording time, esp. by mechanical means, usually with hands or changing numbers to indicate the hour and minute: not designed to be worn or carried about

clock in American English 2
a woven or embroidered ornament on the side of a sock or stocking, going up from the ankle
noun: a short embroidered or woven ornament on each side or on the outer side of a sock or stocking, extending from the ankle upward
transitive verb: to embroider with such an ornament

clock in British English 1
noun: a timepiece, usually free-standing, hanging, or built into a tower, having mechanically or electrically driven pointers that move constantly over a dial showing the numbers of the hours

clock in British English 2
noun: an ornamental design either woven in or embroidered on the side of a stocking

clock in Electrical Engineering
noun: A clock is the basic timing signal in a digital system.