rescind, repeal, countermand, revoke, avoid, nullify, invalidate, reverse, overturn, quash, more...

confirm, validate, ratify

annulment, dissolution, nullity, more...

cancel or set aside,   to cancel out,   declare invalid,   reduce to zero,   to make invalid,   declare invaild,   make null and void,   legally cancel,   abrogate"",   to cancel something