cancellation the act of cancelling; calling off some arrangement
derogation (law) the partial taking away of the effectiveness of a law; a partial repeal or abolition of a law; "any derogation of the common law is to be strictly construed"
A repeal is the removal or reversal of a law. This is generally done when a law is no longer effective, or it is shown that a law is having far more negative consequences than were originally envisioned. If a campaign for the repeal of a particular law gains particular moment, an advocate of the repeal might become known as a "repealer".