Keep it under wraps
To keep something secret or hidden.

Bite your tongue
To stop yourself from saying something that might reveal a secret.

Behind closed doors
Something that happens in secret, away from public view.

Let the cat out of the bag
To accidentally reveal a secret.

A well-kept secret
A secret that has been successfully hidden.

In the loop
Being informed about something, especially a secret.

The skeleton in the closet
A secret that could bring embarrassment or scandal if revealed.

Spill the beans
To reveal a secret, often accidentally.

Keep something under your hat
To keep something a secret.

On the hush-hush
Something done secretly.

Out of the loop
Not informed about something, especially a secret.

Let sleeping dogs lie
To avoid mentioning a secret or problem that could cause trouble.

The tip of the iceberg
A small, visible part of a much larger secret or problem.

Keep a secret
To not tell anyone about something that is supposed to be confidential.

Under the radar
Something that is done quietly or secretly, without drawing attention.

In the dark
To be unaware of something secret or hidden.

Blow the whistle
To reveal a secret, especially about wrongdoing.

Keep your cards close to your chest
To keep your plans or ideas secret.

Secrets don’t make friends
Keeping secrets can lead to mistrust and distance in relationships.

Peeling back the layers
Gradually revealing a secret or hidden truth.