An Etymological Dictionary of the German Language/Annotated/bleichen
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bleichen, verb, ‘to lose colour,’ erbleichen, ‘to grow pale,’ from Middle High German blîchen, ‘to shine, blush,’ Old High German blîhhan; compare Anglo-Saxon blîcan, Middle English blîken, ‘to turn pale’; Old Icelandic blíkja, ‘to appear, shine, lighten.’ The i root of Slavonic bliskati, ‘to sparkle’ (for *bligskati), blěskŭ, ‘splendour,’ Lithuanian blaivýtis, ‘to clear up,’ is more closely connected with the word than the e root in φλέγω, ‘to burn, flame.’ The pre-Teutonic form of the root was perhaps bhlig, meaning ‘lustre’ (compare also Blech, bleich; further Old High German blick, see Blitz). —