An Etymological Dictionary of the German Language/düster
düster, adj. (unknown to UpG.?), ‘gloomy, dismal, sad,’ from the equiv. LG. düster, dûster; comp. OSax. thiustri, AS. þeóstre, þŷstre, ‘dark,’ MidHG. dinster, OHG. dinstar, OHG. finstar, OSax. finistar are remarkable parallel forms expressing the same idea; so too AS. þeóstru, ‘darkness.’ The primary form may be seen in the stem of dämmern, Goth. *þimis, ‘twilight,’ OInd. támas, ‘darkness’; Lat. tenebrae (for *temebrae) comes nearest perhaps to MidHG. dinster. f is interchanged with þ in Fackel, AS. þœcele; in the same way finster might be related to dinstar (from þinstar). These guesses are, however, too uncertain.