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in- (1), im- A negation prefix indicating "not" or "against."

From Latin in- 'id.' From Proto-Italic *in- 'id.' From Proto-Indo-European *n̥- 'id.'

Italic: Oscan an-, Umbrian a-

Indo-European: Celtic: Old Irish in-, Old Welsh an-, Old Breton an-, Old Cornish an-; Germanic: Gothic un-, Old Norse ó-, Old High German un-, Old Saxon un-, Old English un- (English un-); Hellenic: Ancient Greek ἀν- (án-); Indo-Iranian: Sanskrit an-, Avestan a-; Tocharian: A an-, B an-