power of attorney 
noun [mass noun] Law
The authority to act for another person in specified or all legal or financial matters.If he was told there was such a veto power or power of attorney, why did he not ask to see proof of same....
- We've had conversations about her wishes; I have both financial and medical power of attorney for her, should it become necessary, and I'm the executor of her will as well.
- There, the wife was not involved in the company, she was not a company director, her husband was simply temporarily incapacitated and she had power of attorney.