内密|ないみつnaimitsu[0]heiban (flat)

1. na-adjective, no-adjectiveprivacy; secrecy; confidentiality
   この情報じょうほうは内密ないみつにしてください。↗

   Keep this information under your hat.

• Synonym秘密ひみつNeutralThe everyday default with the widest range: it covers anything kept from others, while 「内密」 is specifically about not letting matters become public.
• Synonym非公開ひこうかいWrittenWritten register: stresses that something is not open to the general public; typical of documents and meetings rather than everyday talk.
• Synonym機密きみつWrittenWritten register: important secrets of organizations or the state; the degree of secrecy is heavier than 「内密」.
• Synonym内々うちうちNeutralNeutral: handling something only among one's own circle, common even in business and formal settings, as in 「内々に打診する」; 「内密」 stresses keeping it from outsiders.
• Synonym内緒ないしょNeutralColloquial: keeping something hidden from others, as in 「内緒にしてね」. It is the casual everyday word, where 「内密」 is about not letting things go public.
• Synonym密かひそかWrittenWritten: secretly or stealthily, usually as the adverb 「密かに」; it stresses that an act goes unnoticed, while 「内密」 is about not making it public.
• RelatedプライバシーNeutralA neutral loanword for privacy: it is about one's personal life being left alone, not about keeping specific matters secret the way 「内密」 is.
• Related隠密おんみつWrittenWritten and more old-fashioned than 「内密」: doing something covertly, and by extension the spies of the Edo period.
• Related秘めやかひめやかWrittenWritten and rare, with a literary flavor: it describes something quietly hidden, especially feelings, rather than matters handled discreetly like 「内密」.
• Related機密性きみつせいWrittenWritten: the degree to which something must be kept confidential, a property noun common in information security.
• Related秘め事ひめごとWrittenWritten and rare: a hidden matter, often with an intimate or romantic undertone, unlike the neutral discretion of 「内密」.
• Related秘ひWrittenWritten: a single character seen on confidentiality stamps on documents; rarely used on its own.
• Antonym公表こうひょうWrittenAntonym, written register: a formal announcement making something publicly known — the opposite of keeping a matter 「内密」.
• Antonym公開こうかいNeutralAntonym, neutral: opening something up so anyone can see it, the opposite of keeping it 「内密」.

Use 「内密」 for keeping something from going public and handling it quietly, as in 「内密にお願いします」 or 「内密に処理する」. For everyday secrets, 「秘密」 and the colloquial 「内緒」 are the usual choices; 「内々」 covers matters kept within one's own circle. 「非公開」 fits documents and meetings, 「機密」 and 「機密性」 organizational and security contexts, while 「公表」 and 「公開」 are the opposites.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 秘密ひみつにすること。内緒ないしょ。