To repeat data on purpose so it is faster to read. Denormalising trades one truth for many copies of it.
Latin de- (reversal) + normalis (made according to a rule), from norma (a carpenter's square, rule, pattern); to repeat data on purpose so it reads faster, trading a single truth for several copies of it.
Norma is a carpenter's square, the tool a rule is checked against, and denormalizing deliberately sets that tool aside for speed. Every copy made this way is a small bet that none of them will ever need to disagree.