Behalf

wiktionary

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From Middle English bihalve(“nearby”), from Old English bī healfe(“by [his/her] side”), from bī(“by”) + healfe(“side, half”), equivalent to be- +‎ half.

etymonline

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behalf (n.)

c. 1300, behalve (with dative suffix), "for the sake or benefit, advantage, interest" (of someone), from Old English (him) be healfe "by (his) side," and, incorrectly, from on (his) healfe "on (his) side," from healfe "side" (see half). The word was confused with Middle English behalve, behalves (adv. and prep.) "by the side of, near."