An Etymological Dictionary of the German Language/lehren
lehren, vb., ‘to teach,’ from MidHG. and OHG. lêren, ‘to instruct, teach, make one acquainted with,’ sometimes also ‘to learn’; corresponding to Du. leeren, AS. lœ̂ran (whence OIc. lœ̂ra is borrowed), Goth. laisjan, ‘to teach.’ A common Teut. vb. with the primit. meaning ‘to cause to know’; laisjan is the factitive of a pret. pres. lais, ‘I know,’ preserved in Goth. only. In G. and E. only a partic. derivative was retained, which was probably represented in Goth. by *lisnan or *liznan; comp. lernen. Allied also to Goth. leis, ‘knowing,’ leisei, ‘knowledge,’ in lubja-leis, -leisei, ‘skilled in poisons, witchcraft.’ We have data for assuming that Goth. lais, ‘I know,’ is based on a prim. meaning ‘I have experienced,’ for the stem lis of lehren and lernen appears also in Gleise and leisten in the old sense of ‘to go,’ with which Lat. lîra, ‘furrow,’ and its derivative delîrare (lit. ‘to slip away from’) are connected, as well as OSlov. lěcha, ‘ridge (of a furrow),’ mentioned under Gleise; comp. leisten. —