Source : Webster's Revised Unabridged Dictionary (1913)

Nullifier \Nul"li*fi`er\, n.
   One who nullifies or makes void; one who maintains the right
   to nullify a contract by one of the parties.

Source : WordNet®

nullifier
     n 1: an advocate of nullification; someone who believes that a
          state can resist federal laws
     2: an official who can invalidate or nullify; "my bank check
        was voided and I wanted to know who the invalidator was"
        [syn: {invalidator}, {voider}]