in
The origin and history of in.
Etymology
This word goes back to the PIE word *h₁en. As a preposition and verb, it comes from Middle English in, from Old English in, from Proto-Germanic *in. As an adverb, noun and adjective, it comes from Middle English in, from Old English inn and inne, from Proto-Germanic *innai. Senses 1 and 2, "in" and "into", come from the original PIE prefix, with the locative and accusative case respectively. Senses 3 and 4, "qualification" and "means", come from the PIE metaphor in which all infinitives derive from locatives.
