v. To free from misconception, deception or error.
the GNU version of the Collaborative International Dictionary of English
v. To cause to be no longer deceived; to free from deception, fraud, fallacy, or mistake.
The Century Dictionary and Cyclopedia
To free from deception, cheat, fallacy, or mistake; open one's eyes.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
v. free from deception or illusion
Word Usage
"Their avowed object was to present a petition personally to the Prince Regent, that they might "undeceive" him; as if such a thing were possible, or, being possible, would be of the slightest service."