keep (something) on the down low
To keep something in a state of secrecy or minimal public knowledge; to not share something with anyone else. Keep this on the down-low, but Janet is planning to break up with Kevin next week.
on the down low
In a state of secrecy or minimal public knowledge; being known only by a select few people. Keep this on the down low, but Janet is planning to break up with Kevin next week. My parents know about the pregnancy, but I'd like it to stay on the down low otherwise.