An Etymological Dictionary of the German Language/Annotated/Falter
Falter, masculine, simply Modern High German, ‘butterfly’; the Middle High German term is vîvalter (corrupted also into zwivalter), ‘butterfly,’ from which the Modern High German word has been corrupted by connecting it with falten. But Middle High German vîvalter is based upon an Old Teutonic term for ‘butterfly,’ which may have been *feifaldrô in Gothic; compare Old High German fîfaltra, Old Saxon fîfoldara, Anglo-Saxon fîfealde, Old Icelandic fifrilde, ‘butterfly’; akin to Dutch vijfwouter, ‘a sort of butterfly.’ The origin of this term is not yet established, although it is probably a reduplicated form like beben and zittern.