twelvechairs was explaining the etymology. As current usage goes, it's a British English / American English difference, as has already been pointed out. (And

twelvechairs was explaining the etymology. As current usage goes, it's a British English / American English difference, as has already been pointed out. (And frankly, taking an arbitrary regional spelling difference and declaring that whichever one you're used to is "Right", without even an attempt at a justification, is pointless at best and borderline trollish at worst.)