fifteogoða [OE]
fiftithe [MI]
fiftieth [ME]
fiftieþ
https://www.etymonline.com/word/fiftieth#etymonline_v_39702
https://www.merriam-webster.com/dictionary/fiftieth
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED15902
https://bosworthtoller.com/10685