Where does “mightn't've” come from?

mightn't've (English) comes from English mightn’t, from English -n’t, from English Not, from Middle English not, from Middle English nought, from Old English nōwiht, from Old English ne, from Old English ealles — Creates action nouns or result nouns from verbs;...

mightn't've (English): might not have

Definitions

  1. might not have

Ancestry of “mightn't've”, step by step

mightn't've traces back through two separate lines of ancestry.

via English mightn’t

StepLanguageWordMeaning
1Englishmightn’tmight not (negative auxiliary)
2English-n’t
3EnglishNot
4Middle Englishnotnot; nothing, nought; nobody, no person
5Middle Englishnoughtnothing, none; not; iniquitous, wicked
6Old Englishnōwiht
7Old Englishnenot; or, and not; "ne... ne..." is used to mean "...
8Old Englisheallescompletely, wholly, entirely; totally,...
9Old English-espossessive marker, indicating that an object...
10Proto-Germanic-asused in formation of adverbs
11Proto-Indo-European-ēsPrimarily forms adjectival bahuvrīhi compounds
12Proto-Indo-European-ess
13Proto-Indo-European-osCreates action nouns or result nouns from verbs;...

via English ’ve

StepLanguageWordMeaning
1English’vein its sense marking the perfect or retrospective aspect
Every word from Proto-Indo-European -osEvery word from Old English -esEvery word from Old English ealles