teach

Teach comes from Middle English techen, from Old English tǣċan, meaning to show, declare, or instruct, which traces back through Proto-West Germanic and Proto-Germanic *taikijaną to the Proto-Indo-European root *deyḱ-, meaning to show.

The Old English word already carried a wide range of meanings — to show, warn, prescribe, persuade — and over time these narrowed toward the modern sense of instructing or imparting knowledge. Informally, 'teach' is also now used as a clipped noun for 'teacher.'

It's cognate with German zeigen (to show), and more distantly with Latin dīcō (speak, say) and Ancient Greek deíknumi (to show, explain), all pointing back to that same idea of showing or pointing something out.