Source : Webster's Revised Unabridged Dictionary (1913)

Invalidate \In*val"i*date\, v. t. [imp. & p. p. {Invalidated};
   p. pr. & vb. n. {Invalidating}.] [From {Invalid} null.]
   To render invalid; to weaken or lessen the force of; to
   destroy the authority of; to render of no force or effect; to
   overthrow; as, to invalidate an agreement or argument.

Source : WordNet®

invalidating
     adj : establishing as invalid or untrue [syn: {disconfirming}]