Secret; Secret; Confidential:

Uncover the secrets of the universe;

Uncover the secrets of the universe

The Senate held a closed meeting today.

The Senate held a secret meeting today.

Do it by all means, but keep it strictly confidential.

It must be done, but it must be kept strictly confidential.

Phrases:

Secret report;

Make secret contact with sb.

Secret telegram (message) bamboo telegram; Bamboo wireless;

Secret struggle underground struggle;

Secret meeting; Closed meeting;

Secret activities;

A secret plan;

Secret transactions;

Secret joint eavesdropping;

Secret associations form secret groups;

Secret police;

Secret trade;

Internal cabinet of secret cabinet;

Secret channels;

Secret treaty;

Secret communication and confidential letters;

Voting by secret ballot; Australian votes;

Secret diplomacy;

An unpublished satellite;

Secret documents; Confidential documents;

Secret file indicator back door file indicator;

The secret weapon {Army} [Germany] Uva; Secret weapons;

Confidential information;

Secret protocol knock-out protocol;

Secret election;

Secretly preparing undisclosed reserves;

Secret assets non-ledger assets

Reference: Youdao Dictionary