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®

invalidate
     v 1: declare invalid; "The contract was annulled"; "void a plea"
          [syn: {annul}, {quash}, {void}, {avoid}, {nullify}]
          [ant: {validate}]
     2: of cheques or tickets [syn: {cancel}]
     3: show to be invalid [syn: {nullify}] [ant: {validate}]
     4: take away the legal force of or render ineffective;
        "invalidateas a contract" [syn: {void}, {vitiate}] [ant: {validate}]