bounty (n.)
mid-13c., "generosity," from Old French bonte "goodness" (12c., Modern French bonté), from Latin bonitatem (nominative bonitas) "goodness," from bonus "good" (see bene-). Sense of "gift bestowed by a sovereign or the state" led to extended senses of "gratuity to a military recruit" (1702) and "reward for killing or taking a criminal or enemy" (1764).
I do ... promise, that there shall be paid ... the following several and respective premiums and Bounties for the prisoners and Scalps of the Enemy Indians that shall be taken or killed .... ["Papers of the Governor of Pennsylvania," 1764]