To free someone from deception or false belief; to undeceive or reveal the truth to someone who has been misled.
From dis- (prefix meaning to reverse) + deceive (from Old French decevoir, Latin decipere meaning to ensnare). The dis- prefix creates the opposite action.
Disdeceive is wonderfully logical English—if deceive means to mislead, disdeceive means to unmislead, yet we almost never use it, preferring 'undeceive' or 'disillusion' instead, showing how English sometimes creates synonyms and then picks just one.
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