Where does “PS” come from?

PS (Japanese) comes from German Pferdestärke, from German Pferd, from Middle High German phert, from Old High German pfarifrit, from Old High German parafred, from Latin paraverēdus, from Ancient Greek παρά, from Latin verēdus — horse.

Ancestry of “PS”, step by step

StepLanguageWordMeaning
1GermanPferdestärkehorsepower
2GermanPferdhorse; knight
3Middle High Germanphert
4Old High Germanpfarifrithorse
5Old High Germanparafred
6Latinparaverēdusa horse for travel off public roads or to out of the way places
7Ancient Greekπαρά
8LatinverēdusA fast or light breed of horse; courier's horse; hunter
9Gaulishwerēdoshorse
10Proto-Celtic*uɸoreidoshorse
Every word from Proto-Celtic *uɸoreidosEvery word from Gaulish werēdosEvery word from Latin verēdus