in (one's) behalf

1. As an agent or representative of one; in lieu of one. The boss isn't here at the moment, but I'd be happy to sign for the package in her behalf. Our lawyer will be telephoning the department tomorrow in our behalf, to ensure our application goes through as planned. I'm Professor Walton's research assistant, and I have to go retrieve some library books in his behalf.

2. In the interest or for the benefit of one. It's quite common, even natural, that children don't understand that everything their parents do is in their behalf. This decision is in your behalf, so don't act so ungrateful! You embezzled money, Dad, and I don't buy that you did it "in your kids' behalf."

in (someone's) behalf

1. As the representative of someone else; in lieu of someone. The boss isn't here at the moment, but I'd be happy to sign for the package in her behalf. Janet is really sick, so I'm going to lead the meeting in her behalf. No, my parents own the house, I'm just watching it in their behalf while they're away.

2. In the interest or for the benefit of someone else. Children don't understand until they're older that everything their parents do is in their behalf. You embezzled money, Dad, and I don't buy that you did it "in your family's behalf." She would do anything in the cat's behalf. She treats Fluffy better than she treats herself!