Trying to see if I can get this question answered before I manage to go home and check the OED (assuming I remember…):
Stone. It means a rock, it means a unit of weight, it’s slang for being drugs (so stooooned, man).
Two questions: How much, in weight, is one stone? And why is someone “stoned” when they’re under the influence? I guess the latter could be a reference to how they look and act – like they were whacked on the back of the head with a rock…
er…Slang for being drugs? snort
Slang for being ON drugs, I should say.
Say ON To Drugs!
1 Stone = 6.35 Kilograms = 14 Pounds = 224 Ounces
Yay! No more going to the OED (and having to hunt down my magnifying glass…)
But I do LOVE that thing. 
Before drugs became popular, being stoned used to mean being drunk.
athene1765, if you’d rather look up words online, here’s a great site:
It has some 18 definitions for stone.
Neat!
I used to use the online OED, but that was while I was a student and it was free to me. Can’t afford the $300/year or so to have it for my own personal use.