A code of silence practiced by the Mafia; a refusal to give evidence to the police about criminal activities WordNet 3.0 & Open English WordNet

Omertà is a Southern Italian code of silence and code of honor and conduct that places importance on silence in the face of questioning by authorities or outsiders; non-cooperation with authorities, the government, or outsiders, especially during criminal investigations; and willfully ignoring and generally avoiding interference with the illegal activities of others. Wikipedia

Code of behaviour usually associated with Italian Mafias. Wikipedia Disambiguation

Southern Italian code of honor and silence Wikidata

A code of silence amongst members of a criminal organization (especially the Mafia) that forbids divulging insider secrets to law enforcement, often also followed outside of the organization in fear of retaliation; extensively, any code of silence. Wiktionary

Code of silence amongst members of the Mafia or other criminal organization. Wiktionary (translation)