An Etymological Dictionary of the German Language/Annotated/tünchen
tünchen, verb, ‘to whitewash, plaster,’ from the equivalent Middle High German tünchen, Old High German tunihhôn, mostly mit chalche tunihhôn. The additional expression in Old High German leads to the assumption that tunihhôn means literally ‘to clothe,’ from Old High German tunihha, ‘dress’ (borrowed, like Anglo-Saxon tunuce, from Latin tunica). The Germans still say eine Wand mit Tünche bekleiden, ‘to give a coat of limewash to a wall’ (compare English to coat and coat). With this agrees Italian intonicare, ‘to plaster, rouge’ (intonico, intonicato, ‘plaster’). Note that Latin tunica, Italian tonica, also signifies ‘covering.’ The Latin-Italian word was borrowed at the beginning of the Old High German period; had it been borrowed earlier it would have appeared as *zunihha in Old High German. It cannot have been introduced much later than Fenster and Turm.