An Etymological Dictionary of the German Language/Annotated/Zwitter
Zwitter (earlier Modern High German Zwiedorn), masculine, ‘mongrel, hermaphrodite, hybrid,’ from Middle High German zwitar, zwëtorn, zwidorn, masculine, ‘hermaphrodite, bastard, half-caste,’ Old High German zwitarn, zwitaran, masculine, ‘nothus, hybris.’ A derivative of zwi-, ‘duplex’ (see zwie-); compare Modern High German dialectic Zwister, ‘hermaphrodite.’ Different forms occur in Old Icelandic (tvítóla) and Danish (tvetulle, ‘hermaphrodite’).