- \ \ [OE] In is a widespread preposition amongst the Indo-European languages. Greek had en, Latin in (whence French and Italian en and Spanish in), and amongst modern languages German and Dutch have in, Swedish i, Welsh yn, and Russian v, all of which point back to an original Indo-European *en or *n. The adverb in was not originally the same word; it comes from a conflation of two Old English adverbs, inn and inne, both ultimately related to the preposition in. (An inn is etymologically a place ‘in’ which people live or stay.)\ \ Cf.⇒ INN
Word origins - 2ed. J. Ayto. 2005.