on someone's behalf

noun

1. interest, part, benefit, or respect (only in the phrases on (someone’s) behalf, on or US and Canadian in behalf of, in this (or that) behalf)

n.c.1300, behalve (with dative suffix), from Old English (him) be healfe “by (his) side,” and on (his) healfe “on (his) side,” from healfe “side” (see half). see in behalf of.