OprindelseEither revived or borrowed from Old Norse forn or Swedish forn respectively. from Proto-Germanic *fernaz (“foregoing, previous; recent”), from Proto-Indo-European *perǝm-, *perǝ- (“fore, first”), from Proto-Indo-European *per- (“forth, over, across, through”). A inherited version from Old Danish forn (“old, weak”) went out of use, and was replaced by the more commonly used adjective gammel.
Kilde: Wiktionary