undeclare

un- +‎ declare

undeclare (third-person singular simple present undeclares, present participle undeclaring, simple past and past participle undeclared)

1. (transitive) To reverse the process of declaring; to unsay.
   • 2007 February 4, Noah Feldman, “Whose War Powers?”, in New York Times‎:

     The Constitution gives Congress the power to declare war; but does that include the power to undeclare it?

2. (transitive, programming) To revoke the declaration of (a variable, namespace, etc.) so that it is no longer available.

• Aden ulcer, uncleared