in
The origin and history of in.
Etymology
PIE word *h₁en Preposition and verb from Middle English in, from Old English in, from Proto-Germanic *in. Adverb, noun and adjective from Middle English in, from Old English inn and inne, from Proto-Germanic *innai. Sense 1/2 "in"/"into" are from the original PIE prefix, with locative/accusative case respectively. Sense 3/4 "qualification"/"means" are from the PIE metaphor of all infinitives coming from locatives.