/ ˌnɑːn.dɪˈskloʊ.ʒɚ / noun formal
a situation in which information is not made known to others:
In some cases, the safety of witnesses required the non-disclosure of their identity.
secrecy

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/ ˈsiː.krə.si / noun
the state of being secret or of keeping something secret:
The content of her report is shrouded in secrecy . 她的報告內容依然保秘。
secretiveness

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/ ˈsiː.krə.t̬ɪv.nəs / noun mainly disapproving
the quality or fact of hiding your feelings, thoughts, intentions, and actions from other people:
I don't see the need for all this secretiveness. 我不明白為什麼需要如此保密。
keep (sth) quiet C2 phrase
to try to stop other people from finding out about a fact:
She managed to keep the operation quiet for a while. 她設法令該行動在一段時間內保密。
enshroud

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/ ˈsiː.krət / B1 adjective
If something is secret, other people are not allowed to know about it.
The president escaped through a secret passage underneath the parliament building. 總統從議會大廈下的秘密通道逃跑了。
classified

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/ ˈklæs.ə.faɪd / adjective
Classified information is officially stated to be secret.
These documents contain classified material. 這些文件中有機密資料。
undisclosed

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/ ˌʌn.dɪsˈkloʊzd / adjective
If official information is undisclosed, it is secret.
The meeting is taking place at an undisclosed location. 會議在一個秘密地點召開。
restricted

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/ rɪˈstrɪk.t̬ɪd / adjective
A restricted document is one that you need official permission to read because the government wants to keep it secret.
unidentified

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/ ˌʌn.aɪˈden.t̬ə.faɪd / adjective
whose name is not known or is being kept secret:
Police are investigating the death of an unidentified man whose body was found yesterday. 昨天發現一具無名男屍,警方正在調查這宗案件。
closeted

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/ ˌblaɪnd ˈtrʌst / noun
a financial arrangement in which someone's money is invested for them by another person or company, who controls and makes all decisions about the investments:
If he is elected, his assets should go into a blind trust so there is no possible conflict of interest. 如果他當選,其資產應該進行全權信託,這樣就不會產生利益衝突。
/ ˈprɪv. ə l.ɪdʒd / adjective specialized
Priviledged information is secret and does not have to be given even in a law court.

(Translation of 保密 from the Cambridge Chinese (Traditional)-English Dictionary © Cambridge University Press)