das Maul halten
"Das Maul halten" is a crude German colloquialism that functions both as a blunt command to be quiet and as a description of deliberate silence or secrecy. Choosing the right English equivalent depends on context and how much of the original bluntness needs to come through.
1. to shut up [colloquial]
The most natural equivalent in command contexts: blunt and widely understood, though slightly rude.
2. to keep one's mouth shut [colloquial]
Used when the emphasis is on staying quiet about something specific, less aggressive than a direct command, closer to deliberate secrecy.
Notes
"Maul" literally refers to an animal's snout; applied to a person it is deliberately dehumanising. The polite German counterpart is "den Mund halten". If you want to mirror the full crudeness in English, "keep your trap shut" or "zip it" are good options; for most everyday contexts "shut up" already carries the same punch.