Benefit

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late Middle English (originally denoting a kind deed or something well done): from Old French bienfet, from Latin benefactum ‘good deed’, from bene facere ‘do good (to)’.

wiktionary

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From Late Middle English benefytt, benefett, alteration (due to Latin bene-) of benfet, bienfet, bienfait(“good or noble deed”), from Anglo-Norman benfet(“well-done”), Middle French bienfait, from Old French bienfet, bienfait(“foredeal, favour”), from past participle of bienfaire(“to do good, do well”), from bien(“well”) + faire(“to do”), modelled after Latin benefactum(“good deed”). More at benefactor.

etymonline

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benefit (n.)

late 14c., benefet, "good or noble deed; helpful or friendly action," also "a beneficial thing; advantage, profit," from Anglo-French benfet (Old French bienfait), from Latin benefactum "good deed," from bene facere, from bene "well" (see bene-) + facere "to do" (from PIE root *dhe- "to set, put"). Meaning "public performance or entertainment to raise money for some deserving unfortunate person or charitable cause" is from 1680s.

benefit (v.)

"do good to, be of service," late 15c., from benefit (n.). Related: Benefited; benefiting.