Where does “un” come from?

un-1
Word Origin
See more synonyms on Thesaurus.com
1.
a prefix meaning “not,” freely used as an English formative, giving negative or opposite force in adjectives and their derivative adverbs and nouns ( unfair; unfairly; unfairness; unfelt; unseen; unfitting; unformed; unheard-of; un-get-at-able), and less freely used in certain other nouns ( unrest; unemployment).
Expand
Compare un-2.
Origin of un-1 Expand
Middle EnglishOld EnglishMiddle English un-, on-, Old English; cognate with Dutch on-, Gothic, German un-, Old Norse ū-, ō-; akin to Latin in-, Greek an-, a-. See a-6, an-1, in-3
Synonym Study Expand
See in-3.
un-2
1.
a prefix freely used in English to form verbs expressing a reversal of some action or state, or removal, deprivation, release, etc. ( unbend; uncork; unfasten, etc.), or to intensify the force of a verb already having such a meaning ( unloose).
Expand
Compare un-1.
Origin Expand
Middle English, Old English un-, on-; cognate with Gothic and-, Dutch ont-, German ent-; akin to Latin ante, Greek antí; cf. ante-, anti-