late 14c., how so evere "no matter how, however," an emphatic form of how-so "in what(ever) way" (late Old English hu se), from how (adv.) + so (adv.); + ever.
A parallel and earlier form in Middle English was howsomever (early 14c.), which survived through 18c. in provincial English and after that was counted a vulgar Americanism by English writers; it is the same compound but with the obsolete conjunction sum, from Old Norse sem "as, that" (cognate with Danish and Swedish som) in place of so.