An Etymological Dictionary of the German Language/Annotated/fliehen

by Friedrich Kluge

fliehen, verb, ‘to flee,’ from the equivalent Middle High German vliehen, Old High German fliohan; corresponds to Old Saxon fliohan, Anglo-Saxon fleón (from fleóhan), English to flee, Old Icelandic flýja; the f before l is a common substitution for an older initial þ, as in flehen (Gothic þlaihan), flach (from Gothic þlaqus); compare Gothic þliuhan, ‘to flee.’ This older form was retained only in Gothic; Scandinavian has f (flýja), like the West Teutonic verbs. Hence the Teutonic root is þluh, and by a grammatical change þlug, pre-Teutonic root tluk, tleuk. Fliegen is primitively allied, since it is based upon the root plugh. In the earliest Old Icelandic and in West Teutonic the forms of both the verbs must undoubtedly have been confused; thus Old Icelandic flugu and Anglo-Saxon flugon in the earliest period may mean ‘they fled’ and ‘they flew.’ See Flucht.