rotund

Rotund is a learned borrowing from Latin rotundus, meaning "round," which comes from Latin rota, "wheel." That in turn traces back to the Proto-Indo-European root *Hreth₂-, meaning "to run" or "to roll."

The word entered English directly from Latin as a formal, bookish way to say "round," keeping close to its original sense of roundness rather than shifting meaning over time.

Rotund is a doublet of round — the two words descend from the same root, but round arrived through a different, less formal path into English while rotund kept its Latin shape.