An Etymological Dictionary of the German Language/fluchen
fluchen, vb., from the equiv. MidHG. vluochen, OHG. fluohhôn, ‘to curse, imprecate,’ with an existent str. partic. OHG. farfluohhan, ‘depraved, wicked’; comp. OSax. farflôken, ‘accursed’; Goth. flôkan (not *flêkan), str. vb., ‘to lament,’ Du. vloeken, ‘to curse, execrate,’ In E. and Scand. the Teut. root flôk does not occur. Goth. flôkan, ‘to lament, bewail,’ shows the earlier meaning of the cognates; the root flôk, from pre-Teut. plâg, may be connected with Lat. plangere, ‘to strike, mourn,’ Gr. root, πλαγ in πλήσσω (ἐξεπλάγη), ‘to strike.’ The Lat. verb facilitates the transition of the meaning ‘to strike,’ ‘to lament,’ then ‘to imprecate, curse.’ —