Definitions of blank check
(pejorative) when someone has given you either unlimited freedom to do what you want or unlimited money to spend what you want, especially on a project, scheme, or plan etc
The Prime Minister gave a blank check to Nepal to come up with its own proposals.
a check (=a written order for a bank to pay money) that has been signed but on which the amount has not be stated
She gave a blank check to the cashier and asked him to fill in the amount.