The story
- Proto-Germanic · inherited from*gagin“towards, against”
- Proto-West Germanic · inherited from*gagin
- Old English · inherited fromgeġn-
- Middle English · inherited fromgain-
- English todaygain-
From Middle English gain- (prefix), from Old English geġn-, gēan- (“back, against, in return”, prefix), from Proto-West Germanic *gagin, from Proto-Germanic *gagin (“towards, against”). Cognate with Saterland Frisian juun- (“counter-”), West Frisian tsjin- (“counter-”), Dutch tegen- (“counter-”), German gegen- (“against, toward, at”), Icelandic gagn- (“through”). More at again.
Etymology from Wiktionary, CC BY-SA 4.0.