Gain
late 15th century (as a noun, originally in the sense ‘booty’): from Old French gaigne (noun), gaignier (verb), of Germanic origin.
wiktionary
From Middle English gayn, gain, gein(“profit, advantage”), from Old Norse gagn(“benefit, advantage, use”), from Proto-Germanic *gagną, *gaganą(“gain, profit", literally "return”), from Proto-Germanic *gagana(“back, against, in return”), a reduplication of Proto-Germanic *ga-(“with, together”), from Proto-Indo-European *ḱóm(“next to, at, with, along”). Cognate with Icelandic gagn(“gain, advantage, use”), Swedish gagn(“benefit, profit”), Danish gavn(“gain, profit, success”), Gothic 𐌲𐌰𐌲𐌴𐌹𐌲𐌰𐌽( gageigan, “to gain, profit”), Old Norse gegn(“ready”), dialectal Swedish gen(“useful, noteful”), Latin cum(“with”); see gain-, again, against. Compare also Middle English gaynen, geinen(“to be of use, profit, avail”), Icelandic and Swedish gagna(“to avail, help”), Danish gavne(“to benefit”).
The Middle English word was reinforced by Middle French gain(“gain, profit, advancement, cultivation”), from Old French gaaing, gaaigne, gaigne, a noun derivative of gaaignier(“to till, earn, win”), from Frankish *waidanjan(“to pasture, graze, hunt for food”), ultimately from Proto-Germanic *waiþiz, *waiþō, *waiþijō(“pasture, field, hunting ground”); compare Old High German weidōn, weidanōn(“to hunt, forage for food”) (Modern German Weide(“pasture”)), Old Norse veiða(“to catch, hunt”), Old English wǣþan(“to hunt, chase, pursue”). Related to wathe, wide.
From dialectal English gen, gin, short for again, agen(“against”); also Middle English gain, gayn, gein, ȝæn(“against”), from Old English gēan, geġn(“against”). More at against.
From Middle English gayn, gein, geyn(“straight, direct, short, fit, good”), from Old Norse gegn(“straight, direct, short, ready, serviceable, kindly”), from gegn(“opposite, against”, adverb) (whence gagna(“to go against, meet, suit, be meet”)); see below at gain. Adverb from Middle English gayn, gayne(“fitly, quickly”), from the adjective.
Compare Welsh gan(“a mortise”).
etymonline
gain (n.)
c. 1200, gein, "advantage, benefit; help," c. 1300, "reward, profit, that which has been acquired" (possessions, resources, wealth), from Old French gain, gaaigne "gain, profit, advantage; work, business; booty; arable land" (12c.), from Germanic, and from Old Norse (see gain (v.)). Meaning "any incremental increase" (in weight, etc.) is by 1851. Related: Gains. The French word enfolded the notions of "profit from agriculture" and "booty, prey."
gain (v.)
1520s, "obtain as profit," from French gagner, from Old French gaaignier "to earn, gain; trade; capture, win," also "work in the fields, cultivate land," from Frankish *waidanjan "hunt, forage," also "graze, pasture," from Proto-Germanic *waithanjan "to hunt, plunder," from *waithjo- "pursuit, hunting" (source also of Old English waþ "hunting," German Weide "pasture, pasturage," Old Norse veiðr "hunting, fishing, catch of fish").
This is from PIE root *weie- "to go after, strive after, pursue vigorously, desire," with noun derivatives indicating "force, power" (related to *wi-ro- "man;" see virile). Cognates include Sanskrit padavi- "track, path, trail," veti- "follows, strives, leads, drives;" Avestan vateiti "follows, hunts;" Greek hiemai "move oneself forward, strive, desire;" Lithuanian vyti "to chase, pursue;" Old Norse veiðr "chase, hunting, fishing;" Old English OE wað "a chase, hunt."
Meaning "obtain by effort or striving" is from 1540s; intransitive sense of "profit, make gain" is from 1570s. Meaning "arrive at" is from c. 1600. Of timepieces by 1861. Related: Gained; gaining. To gain on "advance nearer" is from 1719. To gain ground (1620s) was originally military.
