An Etymological Dictionary of the German Language/Annotated/Felsen
Felsen, masculine, ‘rock,’ from the equivalent Middle High German vęlse, vęls, masculine, Old High German fęlis, masculine, felisa, feminine (from which French falaise, ‘cliff,’ is borrowed); akin to Old Saxon fęlis, masculine, probably also to Old Icelandic fjall, ‘mountain’; the latter would be *filza- in Gothic, the former *falisa-; in Dutch and English the word is wanting. Old Irish ail (from *palêk), ‘rock,’ Old Slovenian planina, ‘mountain,’ Sanscrit parvata, ‘rock, mountain,’ may be primitively allied. Connected also with Old Indian púr, ‘fastness, citadel,’ to which Greek πόλι-ς has been referred? or with Sanscrit pâšâṇa (for *palsâna), ‘stone’?.