What is the X in X-mas?
early 14c., from Old French frenge "thread, strand, fringe, hem" (early 14c.), from Vulgar Latin *frimbia, metathesis of Latin fimbriae (plural) "fibers, threads, fringe," of uncertain origin. Figurative sense of "outer edge, margin," is first recorded 1894. Related: Fringes. Fringe benefits is recorded from 1952.
late 15c., from fringe (n.). Related: Fringed; fringing.
A benefit, like insurance coverage, added to one's pay; fringe benefit (1960+)