From The Collaborative International Dictionary of English v.0.48 [gcide]:
Usage: These words have in common the idea of setting aside by some overruling act. Abolish applies particularly to things of a permanent nature, such as institutions, usages, customs, etc.; as, to abolish monopolies, serfdom, slavery. Repeal describes the act by which the legislature of a state sets aside a law which it had previously enacted. Abrogate was originally applied to the repeal of a law by the Roman people; and hence, when the power of making laws was usurped by the emperors, the term was applied to their act of setting aside the laws. Thus it came to express that act by which a sovereign or an executive government sets aside laws, ordinances, regulations, treaties, conventions, etc. Revoke denotes the act of recalling some previous grant which conferred, privilege, etc.; as, to revoke a decree, to revoke a power of attorney, a promise, etc. Thus, also, we speak of the revocation of the Edict of Nantes. Annul is used in a more general sense, denoting simply to make void; as, to annul a contract, to annul an agreement. Nullify is an old word revived in this country, and applied to the setting of things aside either by force or by total disregard; as, to nullify an act of Congress. Cancel is to strike out or annul, by a deliberate exercise of power, something which has operative force.
From WordNet (r) 3.0 (2006) [wn]:
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