retrogressus
From LSJ
ἐγώ εἰμι τὸ ἄλφα καὶ τὸ ὦ, ὁ πρῶτος καὶ ὁ ἔσχατος, ἡ ἀρχὴ καὶ τὸ τέλος → I am the Alpha and the Omega, the first and the last, the beginning and the end
rē̆trōgressus: ūs, m. id.,
I a retrograde movement, retrogression of the sun (post-class.), Macr. S. 1, 17.
