An Etymological Dictionary of the German Language/Annotated/fort
fort, adverb, ‘forwards, continuously, away,’ from Middle High German vort, adverb, ‘forwards, further, continuously.’ Old High German *ford is wanting; it would correspond to Old Saxon forth, Anglo-Saxon forþ, English forth; Gothic *faúrþ, and its comparative faúrþis, adverb, ‘formerly’? Fort, Old Teutonic forþ, from an earlier frþo, pṛto, is allied to vor. See fürder, fordern, fördern, and vorder.