ephemeris time vs unit of time

ephemeris time and unit of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
ephemeris time	Yes	No	No	No
unit of time	Yes	No	No	No

As nouns, unit of time is a hypernym of ephemeris time; that is, unit of time is a word with a broader meaning than ephemeris time:

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
unit of time: a unit for measuring time periods

Other hypernyms of ephemeris time include time unit.

ephemeris time (noun)	unit of 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	a unit for measuring time periods