An Etymological Dictionary of the German Language/Annotated/Wittum
Wittum, neuter, ‘widow's jointure,’ the proper term is probably Widetum, neuter. The first component is Middle High German widen, wideme, masculine and feminine, ‘bridal gift, present from the bridegroom to the bride,’ then also ‘endowment of a church,’ Old High German widamo, ‘wedding gift of the bridegroom to the bride.’ The corresponding Anglo-Saxon weotuma, ‘money paid for the bride,’ leads to kinship with Greek ξεδνα, ἕδνον, ‘bridal presents made by the bridegroom,’ to which perhaps Old Slovenian vedą (vesti) and the equivalent Old Irish fedaim, ‘to marry,’ are allied. There is, in any case, no connection between Wittum and the preceding word; compare also widmen.