beneoðan, benyðan [OE]
binethe [MI]
beneath [ME]
benieþ
https://www.etymonline.com/word/beneath#etymonline_v_11034
https://www.etymonline.com/word/be-#etymonline_v_8193
https://www.etymonline.com/word/nether#etymonline_v_6879
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED4675
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED4674/
https://bosworthtoller.com/3681
https://bosworthtoller.com/3661