interest, part, benefit, or respect (only in the phrases on (someone's) behalf, onor US and Canadianin behalf of, in this (orthat) behalf)
Old English be halfe from be by + halfe side; compare Old Norse af halfu
On behalf of is sometimes wrongly used where on the part of is intended. The distinction is that on behalf of someone means `for someone's benefit' or `representing someone', while on the part of someone can be roughly paraphrased as `by someone'. So, the following example is incorrect: another act of apparent negligence, this time not on behalf of the company itself, but on behalf of its banker, when what was meant was there was negligence by the company's banker
For someone else, as someone's agent or representative. For example, In behalf of the board, I want to thank you for your help, or Joan was speaking on behalf of the entire staff. [c. 1300]
For someone's benefit or interest, as in He was collecting the dues in my behalf. [Late 1500s] Some authorities insist that in behalf of be used only to mean “for someone's benefit” and on behalf of only to mean “as someone's agent.” In practice, however, the terms are so often used interchangeably that this distinction no longer has a basis.