An Etymological Dictionary of the German Language/Annotated/Fürst
Fürst, masculine, ‘‘sovereign, chief, prince,’ from Middle High German vürste, masculine, ‘the highest, most distinguished, ruler, prince,’ Old High German furisto, Old Saxon furisto, Dutch vorst, ‘prince’; like Herr, simply a German form. Just as Herr is originally a comparative of hehr, so is Fürst properly a superlat. meaning ‘first’; compare Old High German furist, Anglo-Saxon fyrst, English first, Old Icelandic fyrstr; Gothic *faúrista is wanting; the corresponding comparative is Old High German furiro, ‘the former, preferable,’ Old Icelandic fyrre, ‘former.’ The usual Old Saxon and Anglo-Saxon word for ‘first’ is formo, forma, with the suffix ma (Gothic fruma); from Aryan pṛ like Greek πρόμος, Sanscrit pûrva-s, Old Slovenian prŭvŭ, Lithuanian pírmas, ‘first.’ It is evident that also vor, für, fort, &c., are derivatives of this Aryan root pṛ.