What does annul mean?
The definition of annul
An*nul”, v. t.
[imp. & p. p. Annulled; p. pr. & vb. n. Annulling.]
Etym: [F. annuler, LL. annullare, annulare, fr. L. ad to + nullus none, nullum, neut., nothing. See Null, a.]

1 To reduce to nothing; to obliterate. Light, the prime work of God, to me’s extinct. And all her various objects of delight Annulled. Milton.
2 To make void or of no effect; to nullify; to abolish; to do away with; — used appropriately of laws, decrees, edicts, decisions of courts, or other established rules, permanent usages, and the like, which are made void by component authority. Do they mean to annul laws of inestimable value to our liberties Burke.

Synonyms
— To abolish; abrogate; repeal; cancel; reverse; rescind; revoke; nullify; destroy. See Abolish.