An Etymological Dictionary of the German Language/Annotated/baß
baß (2.), comparative adverb, ‘better,’ from the equivalent Middle High German baȥ, Old High German baȥ; compare Old Saxon bat-bet, Anglo-Saxon bet from batiz (Gothic *batis); it is an old adverb from the adjective discussed under besser. The almost invariable use at present of the adverb besser, instead of the older baß, is due to the fact that the formation of the adverb was no longer understood, and that the adjective at the same time has in every case assumed an adverbial function.