1) Abrogate 2) Annihilate 3) Annul 4) Cancel 5) Destroy 6) Erase 7) Invalidate 8) Negate 9) Override 10) Repeal 11) Stet 12) Undo 13) Void 1) Abrogate 2) Annul 3) Avoid 4) Bring to naught 5) Cancel 6) Declare invalid 7) Invalidate 8) Make void 9) Overturn 10) Quash 11) Render ineffective 12) Repeal 13) Show to be invalid 14) Strike down 15) To make legally invalid 16) To prevent from happening 17) Void 
• (a.) To make void; to render invalid; to deprive of legal force or efficacy. • (a.) To make void; to render invalid; to deprive of legal force or efficacy.
Nul'li·fy transitive verb [ imperfect & past participle Nullified ; present participle & verbal noun Nullifying .] [ Latin nullificare ; nullus none + -ficare (in comp.) to make. See Null , 
verb make ineffective by counterbalancing the effect of; `Her optimism neutralizes his gloom`; `This action will negate the effect of my efforts`
to render or declare legally void or inoperative: to nullify a contract. · to deprive (something) of value or effectiveness; make futile or of no consequence.
[SAT terms] declare invalid declare invalid