inin

In comes from Middle English in ‘inside, within’, from Old English in, from Proto-Germanic *in, and ultimately from Proto-Indo-European *h₁én ‘in’.

1. Proto-Indo-Europeanc. 4500–2500 BCE*h₁én¹‘in’reconstructed
2. Proto-Germanicc. 500 BCE–200 CE*in²reconstructed
3. Proto-West Germanicc. 200–500 CE*in²reconstructed
4. Old Englishc. 450–1150in²
5. Middle Englishc. 1150–1500in²‘inside’
6. Englishearliest quotation c. 1604–1605in²

1. ¹ Wiktionary, Proto-Germanic *in
2. ² Wiktionary, English in
3. Earliest quotation in Wiktionary’s entry: c. 1604–1605, William Shakespeare, All’s Well, that Ends Well: “He that ears my land spares my team and…”.