annul (
http://definr.com/annul)
v 1: declare invalid; "The contract was annulled"; "avoid a plea"
[syn:
invalidate,
quash,
void,
avoid,
nullify]
[ant:
validate]
2: annul by recalling or rescinding; "He revoked the ban on
smoking"; "lift an embargo"; "vacate a death sentence"
[syn:
revoke,
lift,
countermand,
reverse,
repeal,
overturn,
rescind,
vacate]