Wiktionary says : Abbreviation of wollnot or woll + not , negations of archaic form of will .
The Concise Oxford Dictionary of English Etymology agrees: XVII.
contr.
of wonnot , assim.
of wol
not As to other forms, Etymonline only mentions wynnot :
first recorded mid-15c.
as wynnot , later wonnot (1580s) before the modern form [ won't ] emerged 1660s.
english.stackexchange.com/users/300/RegDwigнt
Won’t actually has a pretty interesting and complex history.
Ultimately it does come from a contraction of will and not , but it all happened in a rather roundabout way.
It all started off with the Old English verb willan/wyllan , meaning to will , wish , or want .
Even in Old English it was used occasionally to denote a future intent.
“Ic wille gan” could mean “I want to go” or
“I will go”, depending on context.
Now, the thing about negatives in Old English is that they were often reduced: na(w)ðer = nahwæðer = ne +
hwæðer
neither = not +
whether næfre = ne +
æfre never = not + ever nabbað =
ne + habbað haven’t = have + not We nabbað naðor ne hlaf ne wæter.
We have neither bread nor water.
Not comes from naht via noht .
Related to nawiht meaning naught , it originally meant in no way , but came to be used as an emphatic form of ne .
Subsequently it became unstressed and supplanted ne altogether.
This is an example of Jespersen’s Cycle .
All these things combined led to a new negative form of willan , wynnot .
The past forms of willan began with wold- , which is where we get would .
Under the influence of these forms and the related verb wol , wynnot became wonnot by the late 1500s.
Finally, the modern form won’t emerged by the 1660s as a result of reducing the final vowel in wonnot .
It appears to be the first word so contracted; most of the other -n’t contractions we use today ( can’t , couldn’t , shouldn’t , &c.) arose in the 1700s, modelled after won’t .
In modern English, cannot is the only uncontracted -not compound that survives.
As for the other contractions such as -’ll and -’ve , their history is just as long, though perhaps slightly less convoluted.
But that’s a story for a different question.
;) Also, remember that spelling in Old English was less standardised than in modern English.
There were often several equally valid ways to spell the same word, especially when you took different accents and dialects into account.
So sometimes it’s difficult to get a good historical account of pronunciation and usage changes.
Still, as far as I can tell, this is basically how it went down.
Source:
The Online Etymology Dictionary .
english.stackexchange.com/users/1506/Jon Purdy
It's a contraction of woll not .
english.stackexchange.com/users/12952/Barrie England
A friend found this explanation of the etymology of "will" via Google Books.
I found it interesting.
Will is from the Gothic wilgan, Saxon willan, Dutch willen, German wollen.
Among the various writers cited, I find it written wil, wyl, wyll, wrill, wol, woll.
In Scotland it is often, to this day, pronounced wull, and in some parts of England as if it were written wool!
The past tense was variously written when used as an auxiliary, wold, wolde, wouldin, wulde, would.
The German has present will, imperfect wolte.
Now, as wol and will seem originally to have been the same in meaning, if not in every thing but spelling, and that difference perhaps merely arising from ignorance or conforming to a vicious pronunciation, it does not seem amiss to consider would as derived from will; it certainly is derived from wol, and is as certainly the past tense of will, the auxiliary, to which wol is equivalent, and with which it was interchangeably used.
english.stackexchange.com/users/11958/akent
It was fairly common to form the negative of a word by swapping the first letter (if a consonant) with an "n", or simply adding an "n" if the word started with a vowel.
Chaucer used the word nas to mean "ne was", or "was not".
Nill was the contraction of "ne will", whence willy nilly meaning "willing or unwilling" (or "like it or not").
Nill was driven out by won't .
There are many other examples that have survived — e.g., naught meaning "nothing" is the negative of aught meaning "anything of value".
Neither is the negative of either .
The same thing happened in other European languages.
Willy nilly in Latin is volens nolens .
One and none are ullus and nullus .
In Afrikaans iemand is "somebody", and niemand is "nobody", erens means "somewhere", and nerens means "nowhere".
english.stackexchange.com/users/31498/Michael Horn
Willn't is an archaic version that remains in some dictionaries.
I have no idea if it is in current use.
Once I found it as a teenager, I very, very occasionally used it as a bit of a joke.
english.stackexchange.com/users/19476/Tim
"Don't", "wouldn't", "couldn't" and "isn't" are all contractions of "do not", "would not", "could not" and "is not"... So what's "won't" a contraction of?  It appears to be "will not", but if so, why isn't it " willn't "? (And if there's no good reason, has it  ever  been "willn't" at any point in history?)
What is "won't" a contraction of?
english.stackexchange.com
<etymology><history><contractions><pronunciation-vs-spelling>
english.stackexchange.com/questions/4521
english.stackexchange.com/users/603/Django Reinhardt
Won't is a contraction of "Woll" and "not", with "woll" being an archaic form of "will". However, "willn't" is an archaic form that still exists in some dictionaries. According to Wicktionary the abbreviation of "wollnot" or "woll+not" are negative forms of the archaic form of "will". It originates from the verbs "willan/wyallan" meaning to "will", "wish" or "want". In Old English this could also denote future intent. Finally, the modern form  "won’t"  emerged by the 1660s as a result of reducing the final vowel in  wonnot .Old English spelling was also less standardised, so there were several ways of spelling a word, so it is not always clear historically of its pronunciation and usage.Willn't is an archaic version still in some dictionaries.The source is from the Gothic, Saxon, Dutch and German words.Pronunciation, particularly in Scotland, means "will" is often pronounced like "wool"
Won't is a contraction of "Woll" and "not", with "woll" being an archaic form of "will". However, "willn't" is an archaic form that still exists in some dictionaries. It's a contraction of  woll not, negations of archaic form of  will .   In modern English,  cannot  is the only uncontracted  -not  compound that survives.   In Scotland it is often, to this day,  pronounced wull, and in some parts of England as if it were written  wool!
"Won't" is an abbreviation of  willn't, wollnot  or  woll  +  not, which are negations of an archaic form of  will. Won't is a contraction of "Woll" and "not", with "woll" being an archaic form of "will". However, "willn't" is an archaic form that still exists in some dictionaries.
According to Wicktionary the abbreviation of "wollnot" or "woll+not" are negative forms of the archaic form of "will". It originates from the verbs "willan/wyallan" meaning to "will", "wish" or "want". In Old English this could also denote future intent. Finally, the modern form  "won’t"  emerged by the 1660s as a result of reducing the final vowel in  wonnot . Old English spelling was also less standardised, so there were several ways of spelling a word, so it is not always clear historically of its pronunciation and usage. Willn't is an archaic version still in some dictionaries. The source is from the Gothic, Saxon, Dutch and German words. Pronunciation, particularly in Scotland, means "will" is often pronounced like "wool"
It's a contraction of  woll not, negations of archaic form of  will .    In modern English,  cannot  is the only uncontracted  -not  compound that survives.    In Scotland it is often, to this day,  pronounced wull, and in some parts of England as if it were written  wool!
"Won't" is a contraction of "Woll" and "not", with "woll" being an archaic form of "will". "Willn't" is an archaic form that still exists in some dictionaries.