Wager

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Middle English (also in the sense ‘solemn pledge’): from Anglo-Norman French wageure, from wager ‘to wage’.

wiktionary

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From Middle English wajour, wageour, wager, from Old Northern French wageure, from wagier(“to pledge”) (compare Old French guagier, whence modern French gager). See also wage.

From the verb, wage +‎ -er.

etymonline

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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.)).

wager (v.)

c. 1600 (intransitive); 1610s (transitive), from wager (n.). Related: Wagered; wagering.