The word "teetotaler" is supposed to come from the term "total
abstainer". At one time, the story goes, it was common in
slang to prefix a word with its own first letter to express
emphasis or
definiteness -- hence, a "T-total abstainer". A similar formation in modern slang might be the use of "
period" (or "
full stop") at the end of a sentence to indicate definiteness, as in: "He doesn't drink
alcohol, period."