Both 内緒 (naisho) and 秘密 (himitsu) translate as “secret” in English — but Japanese speakers feel a clear difference between them. One is the light whisper you share with a friend; the other carries real weight, the kind of secret that changes things if it gets out. Learning which to use will make your Japanese sound far more natural — and help you understand the emotional tone of what you hear in dramas, everyday conversation, and song lyrics.
YukaQuick question, Rei — when should I use 内緒 versus 秘密?
ReiAh, a classic mix-up! They’re related but definitely not interchangeable. I’ll explain with examples and it’ll make perfect sense.
At a Glance: 内緒 vs. 秘密
| Feature | 内緒 (naisho) | 秘密 (himitsu) |
|---|---|---|
| Core meaning | A small, low-stakes secret; keeping quiet about something | A serious, confidential secret |
| Kanji | 内緒 | 秘密 |
| Register | Casual / everyday | Neutral to formal |
| Weight | Light — “just between us” | Heavy — “this must not get out” |
| Used in formal contexts? | Rarely | Yes |
| JLPT level | N3 | N3 |
| Common pattern | 〜には内緒で (secretly from ~) | 〜は秘密だ (~ is a secret) |
内緒 (naisho) — The Everyday “Just Between Us”
内緒 comes from Buddhist terminology (内証, inner proof/realization) but today it’s an everyday, casual word. It refers to small secrets, surprises, or things you keep quiet from a specific person. The nuance is light — nobody is in danger, there’s no scandal involved. It’s the word a child uses when hiding a birthday surprise from Mom, or what friends say when sharing a little gossip.
Example 1 — keeping something from someone:
お母さんには内緒でケーキを食べた。
Okaasan ni wa naisho de keeki wo tabeta.
I ate the cake without telling Mom. (secretly from Mom)
Example 2 — asking someone to keep quiet:
これ、内緒にしてね。
Kore, naisho ni shite ne.
Keep this between us, okay?
Example 3 — surprise party context:
田中さんには内緒でパーティーを準備しよう。
Tanaka-san ni wa naisho de paatii wo junbi shiyou.
Let’s prepare a party without Tanaka knowing.
YukaOh interesting! So 内緒 can mean that too? I only knew the basic meaning.
ReiYes! 内緒 is more versatile than most learners realize. Native speakers use it in all sorts of situations — not just the obvious ones.
秘密 (himitsu) — The Serious, Weighty Secret
秘密 is the more formal and heavy word. 秘 (hi) means “hidden / confidential” and 密 (mitsu) means “close / secret.” Together they convey the sense of something deliberately concealed — a government secret, a family scandal, a private matter with real consequences if revealed. 秘密 can be used in casual speech too, but the weight is always heavier than 内緒.
Example 1 — a personal secret:
それは秘密です。
Sore wa himitsu desu.
That is a secret. (I cannot tell you.)
Example 2 — a family secret:
家族の秘密を守らなければならない。
Kazoku no himitsu wo mamoranakereba naranai.
I must protect my family’s secret.
Example 3 — confidential information:
これは会社の秘密情報です。
Kore wa kaisha no himitsu jouhou desu.
This is confidential company information.
YukaWhat about 秘密? Is it used as often as 内緒 in daily conversation?
Rei秘密 is super common too! The two words actually complement each other really well once you understand both.
Side-by-Side Comparison
| Situation | 内緒 (naisho) | 秘密 (himitsu) |
|---|---|---|
| Birthday surprise from a friend | 内緒にしてね ✓ | Possible, but feels heavy |
| State intelligence / national security | ✗ | 国家秘密 ✓ |
| “Don’t tell my boyfriend I bought this” | 彼には内緒で ✓ | Can work, but casual |
| A confidential business deal | Sounds too light | 秘密の取引 ✓ |
| A small white lie to protect someone | 内緒にしておこう ✓ | Possible |
| “What’s your secret?” (to an expert) | ✗ | 秘訣 / 秘密は何ですか ✓ |
Grammar Patterns to Know
Each word has specific grammar patterns that are most natural:
| Pattern | Example | Translation |
|---|---|---|
| 〜には内緒で | 親には内緒で | Without my parents knowing / secretly from my parents |
| 内緒にする | 内緒にしてください | Please keep it a secret |
| 〜は秘密だ | それは秘密だ | That is a secret |
| 秘密を守る | 秘密を守る | To keep / protect a secret |
| 秘密にする | 秘密にしておく | To keep something secret (ongoing) |
| 秘密の〜 | 秘密の場所 | A secret place |
Decision Flowchart: 内緒 or 秘密?
You want to say "secret" in Japanese.
|
v
How serious / sensitive is this secret?
|
_____|_____
| |
LIGHT HEAVY
(casual, (confidential,
everyday, formal, high
fun, stakes, must
low stakes) not leak)
| |
v v
内緒 秘密
(naisho) (himitsu)
Also ask: Are you keeping it FROM a specific person?
→ 〜には内緒で (naisho) is the natural patternQuick Quiz — Test Yourself!
YukaAlright, I think I understand both now. Time for a quiz to check!
ReiThat’s the spirit! Testing yourself is one of the best study techniques. Ready?
Choose 内緒 or 秘密 for each situation.
Q1. You are planning a surprise birthday party for your friend.
田中さんには___でパーティーを計画している。
Tanaka-san ni wa ___ de paatii wo keikaku shite iru.
Answer: 内緒 (naisho)
Reason: A birthday surprise is a light, fun secret — 内緒 is natural here.
Q2. A government document is classified.
その文書は国家___だ。
Sono bunsho wa kokka ___ da.
Answer: 秘密 (himitsu)
Reason: National/government-level secrets always use 秘密.
Q3. “Don’t tell my mom I bought this.”
このこと、お母さんには___にしてね。
Kono koto, okaasan ni wa ___ ni shite ne.
Answer: 内緒 (naisho)
Reason: Casual, low-stakes secret from a specific person — 内緒 fits perfectly.
Q4. “I can’t tell you — it’s a serious secret.”
言えない、本当の___なんだ。
Ienai, hontou no ___ nanda.
Answer: 秘密 (himitsu)
Reason: When emphasizing the gravity or weight of a secret, use 秘密.
Q5. “She secretly went to lunch without telling her boyfriend.”
彼氏には___でランチに行った。
Kareshi ni wa ___ de ranchi ni itta.
Answer: 内緒 (naisho)
Reason: This is a casual, light secret kept from a specific person — the classic 内緒 pattern.
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あわせて読みたい
Secrets often come up in relationship vocabulary. Explore the difference between 浮気 and 不倫 — two words related to romantic betrayal:
Also check out the difference between 本当 and まじ — two ways to say “really” with very different registers:
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