From PIE *h1en — nearly identical in Latin, Greek, German, Welsh, and Sanskrit across 6,000 years, one of humanity's most stable words.
Expressing the situation of being enclosed or surrounded by something.
From Old English in (in, into, within), from Proto-Germanic *in, from PIE *h₁en (in, within). One of the most stable prepositions in the Indo-European family — Latin in, Greek en, Welsh yn, Old Irish in, Lithuanian į, Sanskrit ni all descend from the same PIE form. The root *h₁en carried a sense of enclosure or interiority, denoting
'In' is one of the few English words that is virtually identical to its PIE ancestor *h₁en. Latin 'in,' Greek 'en,' German 'in,' Dutch 'in,' Welsh 'yn' — six thousand years of language change, and the word is still two letters meaning 'inside.' It may be the most phonologically conservative word in any Indo-European language