Omertà

The omertà (Sicilian for manliness) is the vow of silence taken by members of the Italian Mafia.

Particularly, it means that mafiosi will not involve the police or the government in the affairs of the mafia. Joe Valachi was the first person to betray the omertà when he publicly spoke out about the existence of the mafia, when he testified before the United States Congress. Within mafia culture, breaking the oath of omertà is punishable by death.

I was reading this blog post about trains when I came across the term. Although the bad spelling initially led me off the scent, a voyage of discovery through Google later, I am equipped with a new word that I fully intend to overuse in conversation from now on.