Rescind

to declare a contract void from its inception - ab initio, as the Latin fetishists like to say, with the intention of being put in the position one might have been in had the whole ghastly affair never happened in the first place. You might be able to do this if you entered the contract as the result of a false representation but not simply because some raffish oik breached a warranty.

Compare

• terminate which is to seek to put oneself in the place one would have been had your counterpart done what he ought to.