fifta [OE]
fifte [MI]
fifth [ME]
fiþ
https://www.etymonline.com/word/fifth#etymonline_v_5923
https://www.merriam-webster.com/dictionary/fifth
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED15895
https://bosworthtoller.com/10681