gainyoudaoicibaDictYouDict[gain 词源字典]
gain: [15] Gain is Germanic in origin, although English acquired it via Old French. Its distant ancestor is the Germanic noun *waithā. The etymological meaning of this was ‘hunting ground’ (it came ultimately from a prehistoric Indo-European base *wei-, which also produced Lithuanian vyti ‘pursue, hunt’ and Sanskrit veti, vayati ‘seeks, follows’), but gradually this extended via ‘place where food or fodder is sought’ to ‘grazing place’ (its modern German and Dutch descendant weide means ‘pasture’).

From it was formed a verb *waithanjan ‘hunt’ and ‘graze, pasture’, which Vulgar Latin took over as *gwadanjāre. This preserved the semantic dichotomy that had grown up in Germanic: the agricultural sense developed to ‘cultivate land’, and it appears that the ‘hunting’ sense gave rise metaphorically to ‘win, earn’. Both passed into Old French gaaigner, but evidently by the time English acquired the word, the former meaning had all but died out (although it is interesting to note that it was introduced into English as a pseudo-archaism in the 17th and 18th centuries: ‘Of old to gain land was as much as to till and manure it’, Termes de la ley 1708).
[gain etymology, gain origin, 英语词源]
gain (n.)youdaoicibaDictYouDict
late 15c., "that which has been acquired" (possessions, resources, wealth), from Middle French gain, from Old French gaaigne "gain, profit, advantage; work, business; booty; arable land" (12c.), from gaaignier "to gain, earn; capture, win" (see gain (v.)). Meaning "any incremental increase" (in weight, etc.) is by 1851. Related: Gains.

The original French word enfolded the notions of "profit from agriculture" and "booty, prey." Neither the verb nor the noun gain is in Middle English, which however had gainage "profit derived from agriculture" (late 14c., from Old French gaaignage); gaineier "farmer" (late 13c. as a surname); gainerie "a farm" (mid-15c.).
gain (v.)youdaoicibaDictYouDict
1520s, "obtain as profit," from Middle 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" (cognates: Old English waþ "hunting," German Weide "pasture, pasturage," Old Norse veiðr "hunting, fishing, catch of fish"), from PIE *weie- "to strive after, pursue with vigor, desire" (see venison). 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.