An Etymological Dictionary of the German Language/fliehen

by Friedrich Kluge

fliehen, vb., ‘to flee,’ from the equiv. MidHG. vliehen, OHG. fliohan; corresponds to OSax. fliohan, AS. fleón (from fleóhan), E. to flee, OIc. flýja; the f before l is a common substitution for an older initial þ, as in flehen (Goth. þlaihan), flach (from Goth. þlaqus); comp. Goth. þliuhan, ‘to flee.’ This older form was retained only in Goth.; Scand. has f (flýja), like the West Teut. verbs. Hence the Teut. root is þluh, and by a grammatical change þlug, pre-Teut. root tluk, tleuk. Fliegen is primit. allied, since it is based upon the root plugh. In the earliest OIc. and in West Teut. the forms of both the verbs must undoubtedly have been confused; thus OIc. flugu and AS. flugon in the earliest period may mean ‘they fled’ and ‘they flew.’ See Flucht.