'Teach' is PIE *deyk- (to show, point) — kin to Latin 'dicere' (to say) and 'digit' (finger).
To impart knowledge to or instruct someone; to cause to learn by example or experience.
From Old English 'tæcan' (to show, to point out, to instruct), from Proto-Germanic *taikijaną (to show, to point out), from PIE *deyḳ- (to point out, to show). This is the same PIE root that produces Latin 'dicere' (to say, to point out), Greek 'deiknunai' (to show), Sanskrit 'diś-' (to point), and Latin 'digitus' (finger — the pointing instrument). The original sense in Old English was broader
English 'teach,' 'token,' Latin 'digit,' and 'dictionary' all descend from the same PIE root *deyḱ- (to show, point). A teacher shows, a token is a sign shown, a digit is the finger that points, and a dictionary is a collection of things said — and 'to say' in Latin originally meant 'to point out.'