TDT vs ephemeris time

TDT and ephemeris time both are nouns.

Word	Noun	Adjective	Verb	Adverb
TDT	Yes	No	No	No
ephemeris time	Yes	No	No	No

As nouns, TDT and ephemeris time are synonyms defined as:

TDT and ephemeris time: (astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions

Other synonyms of TDT include terrestrial dynamical time, terrestrial time, TT.

TDT (noun)	ephemeris time (noun)
(astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions	(astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions