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GMT

or G.M.T.

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Greenwich Mean Time.

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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

MORE ABOUT GMT

What is GMT?

GMT is short for Greenwich Mean Time, an international reference point for time zones.

How is GMT pronounced?

[ gee-em-tee ]

What does GMT stand for?

Greenwich Mean Time (GMT) is named after Greenwich, a borough outside London, where the British Royal Observatory has kept time since 1675 to aid sailors traveling to the Americas.

Mean time refers to mean solar time, an old method of calculating time based on the position of the sun. Greenwich marks the average time it takes earth to rotate around the sun from noon to noon.

The phrase Greenwich Mean Time is recorded in 1782, the abbreviation GMT in 1840.

In the 19th century, the United Kingdom sought a national time system to use for its railways in place of the numerous local times used by towns and cities, designating GMT in 1880. The United States adopted it in 1883. In 1884, British mapmakers established Greenwich as the prime meridian, where longitude is measured as being 0 degrees.

That same year, 24 time zones were created around the world with GMT as its reference point. Other time zones are plus or minus (ahead of or behind) GMT, making, for instance New York City GMT-5 (hours) but Paris GMT+1.

In 1960, a new universal time standard, now called Coordinated Universal Time (UTC), was mapped onto GMT. They share the same time practice, just that GMT is used as a national time zone by the UK, Ireland, and some African countries, while UTC is simply a reference.

The International Space Station still uses GMT, and GMT is still considered an accurate time in all time zones—pretty impressive considering it is over 300 years old.

How is GMT used in real life?

GMT is the time zone that the U.K. and Ireland, among some other countries, uses outside of Daylight Saving Time (DST). Time just has to be complicated, doesn’t it?

Despite the existence of nation-independent UTC, it is still common practice for people to refer to their own time zone in reference to GMT. GMT is very often used to indicate the time of live events (such as a sports broadcast) for international audiences.

 

More examples of GMT:

“The Wallabies have lost six of their last seven tests. A loss to the Springboks would drop them to their lowest ranking in 15 years. The Rugby Championship match starts at 1005 GMT.”
—Associated Press, September 2018

 

Note

This content is not meant to be a formal definition of this term. Rather, it is an informal summary that seeks to provide supplemental information and context important to know or keep in mind about the term’s history, meaning, and usage.

How to use GMT in a sentence

British Dictionary definitions for GMT

GMT

abbreviation for
Greenwich Mean Time
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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