An Etymological Dictionary of the German Language/Annotated/als

by Friedrich Kluge

als, conjunction, ‘as,’ from Middle High German als, álse, álsô, ‘likewise, thus, as, as if, because,’ hence properly identical with also; Old High German alsô, ‘likewise, like,’ is a compound of al, ‘entirely,’ and sô, ‘thus,’ like the exactly corresponding Anglo-Saxon ealswâ, whence English as, from eal, ‘entirely,’ and swâ, ‘so.’