Greenwich Mean Time vs GMT

Greenwich Mean Time and GMT both are nouns.

Word	Noun	Adjective	Verb	Adverb
Greenwich Mean Time	Yes	No	No	No
GMT	Yes	No	No	No

As nouns, Greenwich Mean Time and GMT are synonyms defined as:

Greenwich Mean Time and GMT: the local time at the 0 meridian passing through Greenwich, England; it is the same everywhere

Other synonyms of Greenwich Mean Time include Greenwich Time, universal time, UT1, UT.

Greenwich Mean Time (noun)	GMT (noun)
the local time at the 0 meridian passing through Greenwich, England; it is the same everywhere	the local time at the 0 meridian passing through Greenwich, England; it is the same everywhere