Etymology
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wager (v.)
c. 1600 (intransitive); 1610s (transitive), from wager (n.). Related: Wagered; wagering.
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wager (n.)
c. 1300, wajour "a promise, a vow, something pledged or sworn to;" also "a bet, a wager; stakes, something laid down as a bet," from Anglo-French wageure, Old North French wagiere (Old French gagiere, Modern French gageure) "pledge, security," from wagier "to pledge" (see wage (n.)).
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stake (v.2)

"to risk, wager, put at hazard or risk upon a future contingency," 1520s, perhaps from the notion of "place a gambling wager on a post" or generally "put up something to be won or lost at a wager" (see stake (n.2)), though Weekley suggests "there is a tinge of the burning or baiting metaphor" in this usage. Related: Staked; staking.

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pari-mutuel 

1881 in reference to a form of betting, from French pari-mutuel "mutual wager," from pari "wager" (from parier "to bet," from Latin pariare "to settle a debt," literally "to make equal," from par, genitive paris, "equal;" see par (n.)) + mutuel "mutual," from Latin mutuus (see mutual (adj.)).

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quinella (n.)
form of betting in which the bettor picks the first and second horses in a given race, 1942, American English, from American Spanish quiniela, originally a ball game with five players, from Latin quini "five each," from quinque "five" (from PIE root *penkwe- "five"). The sense evolution in Spanish was said to be from the game to a wager on the scores of the players, hence "any wager against the house."
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stake-holder (n.)

also stakeholder, 1708, "one with whom bets are deposited when a wager is made," from stake (n.2) + agent noun from hold (v.). Originally one with whom bets are deposited when a wager is made. By 1965 as "one who has something to gain or lose" (in a business, etc.), "one who has an interest in" (something).

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stake (n.2)

"that which is placed at hazard as a wager, the sum of money or other valuable consideration which is deposited as a pledge or wager to be lost or won according to the issue of a contest or contingency," 1530s, perhaps from stake (v.2), which is attested a few years earlier, but both the noun and verb are of uncertain origin. Perhaps literally "that which is fixed or put up," either from a particular use of stake (n.1) "stake, pole," or from the notion of "a post on which a gambling wager was placed" (but OED points out there is "no evidence of the existence of such a custom"). Weekley suggests "there is a tinge of the burning or baiting metaphor" in this usage.

Meaning "the prize in a contest of strength, skill, speed, etc." is by 1620s; plural stakes, "sum of money to be won in a (horse) race," is recorded by 1690s (compare sweepstakes). Meaning "an interest, something to gain or lose" is by 1580s; hence have a stake in "have an interest in the turn of events, have something to gain or lose" (1784). The phrase at stake "state of being laid or pledged as a wager; state of being at hazard or in peril" is from c. 1600.

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gage (v.)
c. 1400, "to deposit as security," from Old French gager, gagier "to guarantee, promise, pledge, swear; bet, wager; pay," from gage "security, pledge" (see gage (n.)). Related: Gaged; gaging. For the measuring sense, see gauge (v.).
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bettor (n.)
"one who lays a wager," c. 1600, also better, agent noun from bet (v.). The form is unusual; OED notes that English agent nouns in -er tend to shift toward -or as their senses become more specific; in this case it also could be to avoid confusion with better (n.1).
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wage (v.)
c. 1300, "give (something) as surety, deposit as a pledge," from Old North French wagier "to pledge" (Old French gagier, "to pledge, guarantee, promise; bet, wager, pay," Modern French gager), from wage (see wage (n.)). Meaning "to carry on, engage in" (of war, etc.) is attested from mid-15c., probably from earlier sense of "to offer as a gage of battle, agree to engage in combat" (mid-14c.). Related: Waged; waging.
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