The Spanish for “to teach,” enseñar comes from the Latin insignare (“to mark”). From the same Latin root, we get the English to sign — signing, after all, is making your mark upon a paper!
But how did signing turn into teaching, in Spanish? Well, think about the English expression… to make a mark on someone. A great teacher truly leaves a lasting mark on you — literally.
The s‑ñ of enseñar maps to the s‑gn of “sign,” with the ñ turning into a gn in English, as it commonly does.