Not pass your lips
Definition 1 of 1
Pro Tip 1/3Secrecy Importance
Use it when highlighting the importance of keeping something confidential. 
This plan must not pass your lips until we announce it officially.
Pro Tip 2/3Emotional Weight
Conveys the serious emotional weight of keeping a secret or staying silent. 
Promise me that my confession will not pass your lips, it's a matter of trust.
Pro Tip 3/3Conversational Context
Often used during conversations to emphasize the expectation of privacy. 
Let's keep this between us; your opinion about the boss should not pass your lips.