From WordNet (r) 2.0 (August 2003) [wn]:
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]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
[1913 Webster]