Keep a/the lid on something
Definition 1 of 2
Pro Tip 1/3Secrecy Importance
Used when hiding information is crucial, often to avoid panic or gossip. 
The government had to keep a lid on the sensitive negotiations.
Pro Tip 2/3Not for Gossip
This phrase is used in serious contexts, not just casual conversations. 
The CEO decided to keep a lid on the merger talks until a deal was reached.
Pro Tip 3/3Protect Reputation
Often involves withholding negative information to maintain a good public image. 
Celebrities must keep a lid on scandals to protect their careers.