seofoþa, seofunda [OE]
sevende, seveth [MI]
seventh [ME]
sevenþ
https://www.etymonline.com/word/seventh#etymonline_v_23300
https://www.merriam-webster.com/dictionary/seventh
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED39691
https://bosworthtoller.com/27467