tomorrow

Tomorrow comes from Middle English tomorwe, from Old English tō morgne, literally "at/on morning" — a fusion of tō ("at, on") and morgne, the dative form of morgen ("morning"). That in turn traces to Proto-Germanic *murganaz, possibly rooted in a Proto-Indo-European word meaning "to blink" or "to twinkle."

The word began as a simple prepositional phrase pointing to the next morning, and over time fused into a single adverb meaning the day after today.

It's built from the same root as "morrow," and its structure has close cousins in other Germanic and Romance languages, such as Dutch and German morgen, Swedish imorgon, Danish i morgen, and French demain.