I've always thought that until was the correct word and till was wrong, like when people use cause for because. Both are words in their own right but with different meanings. However I was reading The Gruffalo today and noticed that it had a 'till' when I would put an 'until'. Are they the same thing?
(Also, am I the only person left who knows the difference between isle and aisle?
Till, until, '*til*. Till, as a variant of until, is a preposition meaning up to the time of. Till—not '*til*, an unnecessary abbreviation—has been in the language for centuries, and there's no reason not to use it. To some it may sound less formal than until, but the two words are interchangeable in almost all contexts.