Like the famous unalienable, which became accepted when some calligrapher misspelt inalienable rights in the final version of US constitution and the dignitaries from the 13 states signed the document.
Actually, that word is from the Declaration of Independence, which predates the Constitution by a number of years.
Also, I'm not so sure it's a misspelling. Searching the various dictionaries at AlphaDictionary shows it means "inalienable," although I haven't found a history of the word as yet. I can't seem to find my
monstrous dictionary at the moment so I can't find an etymology, even at Etymology Online. However, using the tools The Good Doctor and his staff have made available here at AlphaDictionary, I find that both
in- and
un- are prefixes meaning
not, but in the case of
un-:
(adv.) An inseparable prefix, or particle, signifying not; in-; non-. In- is prefixed mostly to words of Latin origin, or else to words formed by Latin suffixes; un- is of much wider application, and is attached at will to almost any adjective, or participle used adjectively, or adverb, from which it may be desired to form a corresponding negative adjective or adverb, and is also, but less freely, prefixed to nouns. Un- sometimes has merely an intensive force; as in unmerciless, unremorseless. (emphasis added)
While the above quote is identified as being " . . . from 1913 Webster's Dictionary and may be outdated," the following one is from the
Compact Oxford English Dictionary:
un-1
• prefix 1 (added to adjectives, participles, and their derivatives) denoting the absence of a quality or state; not: unacademic. 2 the reverse of: unselfish. 3 (added to nouns) a lack of: untruth.
— USAGE The prefixes un- and non- both mean ‘not’, but are used with a difference of emphasis, un- being stronger and less neutral than non-. Compare, for example, unacademic and non-academic in his language was refreshingly unacademic and a non-academic life suits him.
— ORIGIN Old English.
Since the origin of
un- is Old English, which predates the 18th Century by a fair-to-middlin' time period, I'd say it was not a misspelling. But that's just my opinion.
The
National Archives and Records Administration (NARA) has an interesting link:
You will need a better-than-average but not quite arcane vocabulary, or at least access to a
good dictionary, for some of the words in the article, but in general it is not difficult to follow, and gives an insight into late 18th Century rhetoric and logic.