sixteoþa [OE]
sixtenthe [MI]
sixteenth [ME]
sixtínþ
https://www.etymonline.com/word/sixteenth#etymonline_v_48549
https://www.merriam-webster.com/dictionary/sixteenth
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED40598
https://bosworthtoller.com/27905