An Etymological Dictionary of the German Language/lehnen
lehnen (1.), vb., ‘to lean, recline’; it combines MidHG. lënen, linen, intr., ‘to rest (on),’ and (through the medium of MidG.) MidHG. leinen, trans., ‘to lean,’ OHG. linên, earlier hlinên, intr., and leinen, hleinen, trans.; corresponds to AS. hlinian, hleonian, intr., and hlœ̂nan, trans., ‘to lean.’ The real stem is hli, the n is a verbal suffix (in Lehne, however, corresponding to Gr. κλί-νη, a nominal suffix). The graded form of hlī̆, hlai, has been preserved in Leiter; it also existed in an OTeut. *hlaiwaz, *hlaiwiz, n., ‘hill’ (Goth. hlaiw, AS. hlœ̂w, OHG. lêo for hlêo), as well as in Goth. hlains, m., ‘hill,’ OIc. hlein, f., ‘projecting rock.’ The root hlī̆, unpermutated klī̆, appears in the non-Teut. languages with numerous cognates; Gr. κλἷ-νω, ‘to lean,’ κλἷ-μαξ f., ‘ladder, stairs’ (comp. Leiter), κλῖ-νη, ‘couch,’ κλι-σία, ‘conch, easy-chair, tent’ (comp. Goth. hlei-þra, f., ‘tent’), κλι-τύς, ‘hill,’ κλῖ-τος, κλίτος, n., ‘hill’ (comp. ModHG. Leite, f., OIc. hlíþ, f., AS. hlĭþ, n., ‘hill’); Lat. clinare, ‘to incline,’ clivus, m., ‘hill,’ with which are allied Lith. szlýti, ‘to incline to one side,’ szlëti, ‘to lean against,’ szlaítas, ‘slope.’ Hence, according to these allied meanings, the idea is ‘to rise gradually, assume a wry form or a slanting position.’
lehnen (2.), vb., ‘to lend,’ from MidHG. lêhenen, OHG. lêhanôn, ‘to bestow as a fief, lend’; comp. Lehen, and further also leihen; allied to AS. lœ̂nan (pret. lœ̂nde), E. to lend.