GMT vs UT1

GMT and UT1 both are nouns.

Word	Noun	Adjective	Verb	Adverb
GMT	Yes	No	No	No
UT1	Yes	No	No	No

As nouns, GMT and UT1 are synonyms defined as:

GMT and UT1: the local time at the 0 meridian passing through Greenwich, England; it is the same everywhere

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

GMT (noun)	UT1 (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