The story
- Proto-Indo-European*h₁én
- Proto-Germanic*in
- Proto-Indo-European*ǵʰengʰ-
- Proto-Germanic*ganganąder.?
- Proto-Germanic*gagin
- Proto-Germanic*in gagin
- Proto-West Germanic*in gagin
- Old Englishonġēan
- Middle Englishayenes
- English todayagainst
Formed from Middle English ayenes, agenes, againes (“in opposition to”), a southern variant of agen, or directly from again, either way with adverbial genitive singular ending -es; the parasitic -t was added circa 1350, probably by confusion with the superlative ending -est. By surface analysis, again + -st (excrescent ending). Cognate with Saterland Frisian juun (“against”), West Frisian tsjin (“against”), Dutch tegen (“against”), German Low German gegen (“against”), German gegen (“against”), Icelandic gegn (“against”).
Etymology from Wiktionary, CC BY-SA 4.0.