elapsed time vs RTLT

elapsed time and RTLT both are nouns.

Word	Noun	Adjective	Verb	Adverb
elapsed time	Yes	No	No	No
RTLT	Yes	No	No	No

As nouns, RTLT is a hyponym of elapsed time; that is, RTLT is a word with a more specific, narrower meaning than elapsed time:

elapsed time: the time that elapses while some event is occurring
RTLT: the elapsed time it takes for a signal to travel from Earth to a spacecraft (or other body) and back to the starting point

Other hyponyms of elapsed time include one-way light time, OWLT, round-trip light time.

elapsed time (noun)	RTLT (noun)
the time that elapses while some event is occurring	the elapsed time it takes for a signal to travel from Earth to a spacecraft (or other body) and back to the starting point