As long ago as the 1600s in Scotland, the word 'slash' meant a large splash of liquid and - hence also a generous drink - perhaps from the Old French word 'esclache'.
It was not used to mean an act of urination until the 1950s, though the connection with lots of liquid had clearly been made long since
That's a kind comment, Wizard, but a) I have lived for a long time and was well educated...b) I have always been a voracious reader...and c) I am surrounded here by most of the finest reference sources available. Putting all these together can often come up with a result. Cheers
And along with all this great honest opinion, quizmonster, one notices that you're helping people at the unearthly hour of half past seven on a Sunday morning. Well done you!