Is it farther or further?
Old English tæcan (past tense and past participle tæhte) "to show, point out," also "to give instruction," from Proto-Germanic *taikijanan (cf. Old High German zihan, German zeihen "to accuse," Gothic ga-teihan "to announce"), from PIE *deik- "to show, point out" (see diction). Related to Old English tacen, tacn "sign, mark" (see token). Related: Taught; teaching.
Old English tæcan had more usually a sense of "show, declare, warn, persuade" (cf. German zeigen "to show," from the same root); while the Old English word for "to teach, instruct, guide" was more commonly læran, source of modern learn and lore.