"money or other benefit given as a premium or extra pay to reward or encourage work," 1773, a phrase in "Stock Exchange Latin" [Weekley], taken as "a good thing," from Latin bonus "good" (adj.), perhaps originally "useful, efficient, working," from Proto-Italic *dw-eno- "good," probably a suffixed form of PIE root *deu- (2) "to do, perform; show favor."

The correct noun form would be bonum. Specifically as "extra dividend paid to shareholders from surplus profits" from 1808. In U.S. history the bonus army was the name given to the tens of thousands of World War I veterans and followers who marched on Washington, D.C., in 1932 demanding early redemption of their service bonus certificates (which carried a maximum value of $625).

late 14c., bounteuous, bountevous, from Old French bontieus, bontive; see bounty + -ous. Originally "full of goodness to others," but since c. 1400 shading toward "generous in bestowing," a sense which logically might have been left to bountiful. Related: Bounteously; bounteousness.

mid-15c., "liberal in bestowing gifts;" see bounty + -ful. From 1530s as "characterized by bounty, abundant, ample." Related: Bountifully; bountifulness.

Proto-Indo-European root meaning "to do, perform; show favor, revere."

It forms all or part of: beatific; beatify; beatitude; Beatrice; beau; beauty; Bella; belle; beldam; belladonna; belvedere; bene-; benedict; Benedictine; benediction; benefactor; beneficiary; benefice; beneficence; benefit; benevolent; benign; bonanza; bonbon; bonhomie; bonito; bonjour; bonny; bonus; boon (adj.); bounty; debonair; embellish.

It is the hypothetical source of/evidence for its existence is provided by: Latin bene (adv.) "well, in the right way, honorably, properly," bonus "good," bellus "handsome, fine, pretty," and possibly beatus "blessed," beare "to make blessed."