rtlt rss • rtwxrqql · · · Info · Definitions · Synonyms · Characters · · rtlt · · Text Latin · · Script 4 · · Length 1 · · Syllables Definitions · · · (noun) the elapsed time it takes for a signal to travel from Earth to a spacecraft (or other body) and back to the starting point. Synonyms: round-trip light time, RTLT. · · Noun Definition 1 Synonyms · · · round-trip light time · · Synonym 1 Characters · · l latin small letter l U+006C r latin small letter r U+0072 t latin small letter t U+0074