nigontig [OE]
ninti [MI] 
ninety [ME]
nynty
https://www.etymonline.com/word/ninety#etymonline_v_6961
https://www.merriam-webster.com/dictionary/ninety
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED29553
https://bosworthtoller.com/23709