cardinal sin

British  

noun

1. theol any of the seven deadly sins

2. informal  an unforgivable error or misjudgment

   lack of impartiality is considered a cardinal sin in broadcasting circles

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Example Sentences

Perhaps the cardinal sin in Garten’s Thanksgiving guidebook is waiting until the very last minute to prepare and serve your Thanksgiving meal.

From Salon

NBA commissioner Adam Silver has called cap circumvention “a cardinal sin.”

From The Wall Street Journal

For Garrahan, who still defines herself as anti-Peronist, Milei's cardinal sin was to refuse to adjust the budgets of the country's cherished public universities to reflect high inflation.

From Barron's

And viewpoint-based discrimination is a cardinal sin under the First Amendment.

From Slate

NBA Commissioner Adam Silver has called attempts to circumvent it a “cardinal sin.”

From Los Angeles Times