Keep quiet about something
Definition 1 of 1
Pro Tip 1/3Context Matters
Use when information is sensitive or private, and disclosure could cause trouble or distress. 
She decided to keep quiet about her friend's health issues out of respect.
Pro Tip 2/3Not Lies
Keeping quiet doesn't mean lying, but choosing not to share certain details. 
He kept quiet about the surprise party, not wanting to spoil the secret.
Pro Tip 3/3Trust Implications
Demonstrates trustworthiness by showing you can keep a secret when asked. 
My colleagues trusted me to keep quiet about the company's upcoming merger.