in/on behalf of, as a representative of or a proxy for: On behalf of my colleagues, I address you tonight.
2.
in/on (someone's) behalf, in the interest or aid of (someone): He interceded in my behalf.
Origin: 1400–50; late Middle English; Middle English bihalve, earlier as adv. and preposition with the sense “near(by),” orig. as prepositional phrase bi halve on one side; see be-, by, half