From vidvo (“widower”, reconstrued as ‘widow or widower’) + -iĉo (“male”).
vidviĉo (accusative singular vidviĉon, plural vidviĉoj, accusative plural vidviĉojn)
The neologistic suffix -iĉo is controversial, but even among its proponents the word vidviĉo is commonly not recommended. The word vidvo traditionally already means “widower” even without the addition of the masculine suffix -iĉo, making the suffix redundant.
Many users of the term believe that the meaning of vidvo (and other gendered root words) should be changed to have a gender neutral meaning. Other people that actively use it do not aim to change the traditional meaning of “vidvo”, but think the redundancy of -iĉo is preferable to the asymmetry between the forms vidvo (“widower”) and vidvino (“widow”).
See also Gender reform in Esperanto and its section Masculine suffixes on Wikipedia, and the article on -iĉ- in Esperanto.