þridda [OE]
thrid [MI]
third [ME]
þerd
https://www.etymonline.com/word/third#etymonline_v_10760
https://www.merriam-webster.com/dictionary/third
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED45496
https://bosworthtoller.com/32049