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

The cardinal sin of “The Last Days” is that it doesn’t choose a storyline.

From Los Angeles Times

Before Robby and Al-Hashimi engage in any real ideological tussles, though, she commits the cardinal sin of suggesting they change the trauma center’s nickname to something else.

From Salon

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

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

From Slate