What posh English kids (especially at boarding schools) say to each other when they want to stop fighting.
The Latin equivalent to present term mercy.
Often referenced in "The Famous Five" by Enid Blyton.
Julian: "What say you Dick we have a little tussle to see who get's the last cucumber sandwich?"
Dick: "Come on then old chap!"
Dick: "Pax! Oh I say you win Julian"
Julian: "Oh terrific. I'll race you back to Aunt Fanny's!"