Etymology

cp. OIcel gegn ‘straight, direct, ready, serviceable, kindly’ without palatalization of /ɡ/ < PGmc. *gagni- (perhaps ultimately the same stem as that of agayn); cp. OE gēn ‘direct, short’ (recorded once only, at Alex 10.1; see DOE s.v. gegn, gēn), and the adverbial forms OE gegnunga, gēnunga ‘directly, immediately’, (poetic), OE gegnum ‘forward, straight on, directly’, and OS an-gegin, OHG in-gagin.

PGmc Ancestor

*gagni- 

Proposed ON Etymon (OIcel representative)

gegn ‘straight, direct, ready, serviceable, kindly’
(ONP gegn (2) (adj.))

Other Scandinavian Reflexes

Icel gegn, Norw gjegn, ODan gjen, Dan dial gjen, Sw dial gen

OE Cognate

gēn ‘direct, short’ 

Phonological and morphological markers

absence of palatalization of */ɡ/

Summary category

A1*bc

Attestation

In ME, found especially in N and E texts and alliterative verse, but also elsewhere; a Durham place-name in Gain-(see EPNE); modern Sc., N and midland dial.

Occurrences in the Gersum Corpus

Gaw 178, 1241, 1973 etc.; Cl 259, 749; WA 1137, 1318, 3484 etc.

Most editors read the Gaw occurrences at 1214 and 2491 as adjectives, but they could also be parsed as adjectives used nominally (e.g. TGD, McGee).

Bibliography

MED gein (adj.) , OED gain (adj.) , HTOED , EDD gain (adj., adv.1 and sb.1), Dance gayn (a)(adj.), Bj. 151, de Vries gegn (1), Mag. gegn (1), Orel *ʒaʒniz, AEW gegn (1), EPNE gegn, gēn