'blank check' definitions:

Definition of 'blank check'

From: WordNet
noun
Freedom to do as you see fit; "many have doubts about giving him a free hand to attack" [syn: free hand, blank check]
noun
A check that has been signed but with the amount payable left blank [syn: blank check, blank cheque]

Synonyms of 'blank check'

From: Moby Thesaurus