See 63-Across

Clock-setting std.

All clocks are set by it: Abbr.

Prime meridian std.

Clock standard: Abbr.

Clock std.

Intl. standard

Chronometric inits.

You can set your watch by it: Abbr.

Frequent abbr. in BBC announcements

Zulu, in the military: Abbr.

Chronometric std.

London hrs.

Clock setting at 0 degrees longitude: Abbr.

Std. in chronometry

Prime meridian hrs.

Setting for BBC reports, in brief

Certain world std.

Zero-deg. setting

World clock std.

BBC std.

Clock-setting standard: Abbr.

BBC World Service std.

The local time at the 0 meridian passing through Greenwich, England

It is the same everywhere

Time based on a Lon. borough

U.K. time

Basis of std. time

Wikipedia Word definitions in Wikipedia
GMT may mean: Greenwich Mean Time General American Transportation Corporation (GATX), a company which uses GMT as its stock symbol. Generic Mapping Tools in graphical computing Geometric measure theory Giant Magellan Telescope a ground-based telescope planned...