The Collaborative International Dictionary of English v.0.48:

Veto \Ve"to\, v. t. [imp. & p. p. Vetoed (v[=e]"t[=o]d); p.
   pr. & vb. n. Vetoing.]
   To prohibit; to negative; also, to refuse assent to, as a
   legislative bill, and thus prevent its enactment; as, to veto
   an appropriation bill.
   [1913 Webster]