Why is won't the contraction of will not?
Dear Straight Dope:
Willn't you please tell me why the contraction of will not is won't?
Because win't is too weird? Actually, it's because the future tense of the word be, in Old and Middle English, changed with first, second and third person, singular and plural, formal and informal. (All variations are from the Oxford English Dictionary.) The first and third person present forms have shifted among wile, willo, uillo, will, wulle, wule, wolle, woll, and wool for a millenium. The second person went from wilt to wult to woot before becoming obsolete. The plural was something like willen for a bit there. As late as the 19th century, wull and woll were in common use.
Furthermore, the negation, which we might write as will not, was often one word (as is cannot, still used in the 20th century), spelled wynnot, wonnot, woonnot, wo'not, wonot, winnot, we'n't, willn't, willot, and of course won't. As late as the 1849, Charlotte Bronte wrote in Shirley, "That willn't wash, Miss."
Anyway, woll was actually a pretty common form of the word (the past tense of will, if you think about it, is still would rather than willed in most forms), and as the point of contractions is brevity, won't was obviously superior to willn't, saving a syllable in speech and two letters in writing.