An Etymological Dictionary of the German Language/Dünkel
Dünkel, m., ‘fancy, imagination, arrogance, prejudice,’ simply ModHG. Related to the vb. dünken, from MidHG. dunken (pret. dûhte), ‘to seem, appear to,’ OHG. dunchan (chiefly impers. with dat.), ‘to seem’ (pret. dûhta); Goth. þugkjan, þûhta, mostly impers. with dat. ‘to seem’; AS. þyncan, E. to think, which, however, really represents the meanings of AS. þencan, OHG., MidHG. and ModHG. denken. Dünken appears to have been originally a str. vb., of which denken was perhaps the factitive form. The Teut. þunk, þank, is based upon an old Aryan root tng, teng, and this, again, appears in OLat. tongêre, ‘to know’ (comp. Prænest. tongitio, ‘notion’). Comp. denken, Dank.