grave affair

I shall return to the subject after discussing the Osmiae, who are very weighty witnesses in this grave affair.

Had Mistress Underdone a superior, between her and the Countess, whom to offend was a very grave affair?

We felt as though the Rubicon had been passed, and what had commenced as a mere frolic was likely to end as a very grave affair.

She treated it as a very grave affair, and loved it as one of the pleasantest in the course of the day.

A grave affair (affaire), a grave case (cas), is used concerning a criminal rather than a civil process.