eahtatiene, eahtatyne [OE]
ahtene, eightene [MI]
eighteen [ME]
étien
https://www.etymonline.com/word/eighteen#etymonline_v_32176
https://www.merriam-webster.com/dictionary/eighteen
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED13154
https://bosworthtoller.com/8373