An Etymological Dictionary of Astronomy and Astrophysics

A prefix, meaning “behind, after, later, subsequent to, posterior to.”

Etymology (EN): From L. post (adverb and preposition) “behind, after, afterward,” cognate with Gk. (Arcadian and Cyprian dialects) pos “toward, on, at;” Skt. paśca “behind, after, later.”

Etymology (PE): Pasâ-, from pas
“behind” (e.g.: pas-e pardé “behind the curtain”), variant pošt “back; the back; behind;”
Mid.Pers. pas “behind, before, after;” O.Pers. pasā “after;” Av. pasca “behind (of space); then, afterward (of time);” cf.
Skt. paścā “behind, after, later;” L. post, as above;
O.C.S. po “behind, after;” Lith. pas “at, by;”
PIE *pos-, *posko-.