Crossword Genius

Grave offence (8,3)

Ross

I believe the answer is:

cardinal sin

(Another definition for cardinal sin that I've seen is " fundamental foul-up".)

I've seen this clue in The Guardian.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.