in or on behalf of, as a representative of or a proxy for: On behalf of my colleagues, I address you tonight.
2.
in or on (someone's) behalf, in the interest or aid of (someone): He interceded in my behalf.
Origin: 1400–50; late ME; ME bihalve, earlier as adv. and prep. with the sense “near(by),” orig. as prep. phrase bi halve on one side; see be-, by, half
be·half (bĭ-hāf', -häf') n. Interest, support, or benefit.
[Middle English, from Old English be healfe, by (his) side : be, by, at; see by1 + healf, side, half; see half.]
Usage Note: A traditional rule holds that in behalf of and on behalf of have distinct meanings. In behalf of means "for the benefit of," as in We raised money in behalf of the earthquake victims.On behalf of means "as the agent of, on the part of," as in The guardian signed the contract on behalf of the minor child. The two meanings are quite close, however, and the phrases are often used interchangeably, even by reputable writers.
[bi-haf, -hahf] 
