on-gegen, agenes [OE]
against [MI] 
https://www.etymonline.com/word/against#etymonline_v_8020
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED3339
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED30702
https://bosworthtoller.com/024560
https://bosworthtoller.com/24573