An Etymological Dictionary of the German Language/Wittum
Wittum, n., ‘widow's jointure,’ the proper term is probably Widetum, n. The first component is MidHG. widen, wideme, m. and f., ‘bridal gift, present from the bridegroom to the bride,’ then also ‘endowment of a church,’ OHG. widamo, ‘wedding gift of the bridegroom to the bride.’ The corresponding AS. weotuma, ‘money paid for the bride,’ leads to kinship with Gr. ξεδνα, ἕδνον, ‘bridal presents made by the bridegroom,’ to which perhaps OSlov. vedą (vesti) and the equiv. OIr. fedaim, ‘to marry,’ are allied. There is, in any case, no connection between Wittum and the preceding word; comp. also widmen.