From frato (“brother”, reconstrued as ‘sibling’) + -iĉo (“male”).
fratiĉo (accusative singular fratiĉon, plural fratiĉoj, accusative plural fratiĉojn)
The neologistic suffix -iĉo is controversial, but even among its proponents the word fratiĉo is commonly not recommended. The word frato traditionally already means “brother” even without the addition of the masculine suffix -iĉo, making the suffix redundant.
Many users of the term believe that the meaning of frato (and other gendered root words) should be made gender neutral, changing it to “sibling”. Other people that actively use it do not aim to change the traditional meaning of “frato”, but think the redundancy of -iĉo is preferable to the asymmetry between the forms frato (“brother”) and fratino (“sister”).
See also Gender reform in Esperanto and its section Masculine suffixes on Wikipedia, and the article on -iĉ- in Esperanto.