Stories We Like: A Guide to the Comma
early 15c., from Middle French fraternel and directly from Medieval Latin fraternalis, from Latin fraternus "brotherly" (see fraternity). The noun meaning "fraternal twin" is recorded by 1911.
fraternal fra·ter·nal (frə-tûr'nəl)adj.
Of or relating to brothers.
Of, relating to, or being a twin developed from two separately fertilized ova; dizygotic.