As is my wont, I occasionally ruminate upon matters philological and what piqued my interest recently is why “will not” is contracted to “won’t”. Why has the “I” been dropped and replaced by an “o”?
To find the answer, we have to delve into the world of Middle English. The verb “will” appeared in Aelfric of Eynsham’s Grammar, compiled around 995AD, as “wyllan” and acceptable variants included “wil”, “wyll”, “wol”, “woll” and “wole” before spelling conventions were established. The Oxford English Dictionary cites many examples of the verb being spelt as “wole” or “wol” in the 13th century.
As a consequence, contractions to provide the negative included “wynnot”, “wilnot”, “wolnot”, “wilnat” and ”wonnot”. Even though so far as concerned the spelling of the verb the use of an “I” won out, for the contraction of the negative, the “o” from the variant was retained.
One of the earliest uses of “won’t” in print appeared in Thomas Shadwell’s Restoration comedy, The Sullen Lovers, published in 1668, which included the line, “No, no, that won’t do”. Grammarians, stylists, and commentators, though, were appalled by this seemingly illogical contraction, Joseph Addison fulminating in 1711 in The Spectator that “won’t” and other contractions “untuned our language and clogged it with consonants”.
The furore over its use rumbled on for another century before it and its confrères were eventually accepted. Even so, the use of contractions in print is still frowned upon, deemed to be too conversational in tone.
windowthroughtime 
I found this curious myself. Thanks for the explanation.
Interesting that German is ‘wollen’ and Dutch is ‘willen’