v.1. To press down tightly on something: Clamp down the pipe securely before you try to drill a hole in it. I glued the strip of wood to the surface and clamped it down while it dried.
2. To prevent or regulate something with increased strictness: The cartel clamped down on oil production in order to raise prices.
3. To punish or repress someone or something with increased strictness: The government plans to clamp down on tax fraud with tough new laws. Crime began to increase, so the police started clamping down.