Meaning
密 packs four distinct meanings into one character: secrecy, density, closeness, and precision. A confidential document, a tangle of jungle, a close friendship, a rigorous proof — all fall under this single kanji. What links them is the idea of things drawn tightly together, whether that means hidden, compact, intimate, or exact.
密 is built from three stacked components: 宀 (the roof radical, ukanmuri) on top, 山 (mountain) in the middle, and 必 (certainty) at the bottom. Picture something sealed beneath a roof, deep inside a mountain — remote, inaccessible, shut off from the world. 必 adds the sense of something fixed and inescapable. Secrets stay under wraps. Dense matter leaves no gaps. Intimate things are held close. The structure encodes all of this at once.
With 11 strokes, 密 is introduced in 6th grade (小学校6年生) and tested at JLPT N1 — the highest level. It appears constantly in news articles, legal documents, academic writing, and literature. Its compound words reward early study.
Four domains cover the full range. In law and social life: secret or confidential (秘密, 機密). In the physical world: dense, tightly packed, or sealed (密度, 密封). In relationships: intimate and deeply bonded (親密). In academic and scientific writing: precise, rigorous, meticulous (厳密, 緻密).
Readings
On'yomi (音読み) — Chinese-derived readings
ミツ (MITSU) is the reading you'll see in almost every compound. One pronunciation pattern to know: when 密 comes before a consonant-initial syllable, the final -tsu gets absorbed and the next consonant doubles. So 密接 → みっせつ (missetsu) and 密集 → みっしゅう (misshuu). Once you recognize this doubling, it becomes automatic across the vocabulary.
Key compound words using the on'yomi ミツ:
- 秘密 (himitsu) — secret; something kept hidden from others
- 密度 (mitsudo) — density; degree of compactness or concentration
- 親密 (shinmitsu) — intimacy; a close and affectionate relationship
- 厳密 (genmitsu) — strict, precise, rigorous, exact
- 密接 (missetsu) — closely connected; tightly related
Kun'yomi (訓読み) — Native Japanese readings
ひそ.か (hisoka) appears mainly as 密かに (hisoka ni) — "secretly" or "stealthily." It's a literary reading found in novels and formal prose, rarely in casual speech. The nuance is quietly doing something away from others' notice — often with a romantic or dramatic undertone. The dot in ひそ.か simply marks where the kanji reading ends and the okurigana begins.
Key words using the kun'yomi ひそ.か:
- 密かに (hisoka ni) — secretly, stealthily, quietly without drawing attention
- 密かな恋 (hisoka na koi) — secret love; hidden feelings kept to oneself
- 密かな野心 (hisoka na yashin) — secret ambition; hidden aspiration
Common Words & Compounds
密 forms a large family of compound words. Here are the key ones grouped by theme.
Secrecy and Confidentiality
- 秘密 (himitsu) — secret; private information kept from others
- 機密 (kimitsu) — classified information; a state or corporate secret requiring protection
- 密告 (mikkoku) — tipping off authorities; secretly reporting someone to police or officials
- 密偵 (mittei) — secret agent; an informant working undercover
- 密約 (mitsuyaku) — secret agreement; a covert pact made without public disclosure
- 密輸 (mitsuyu) — smuggling; illegal importation or exportation of goods
Density and Physical Compactness
- 密度 (mitsudo) — density; how closely packed matter or population is within a space
- 密集 (misshuu) — dense clustering; crowding together in a concentrated mass
- 密林 (mitsurin) — dense forest; jungle where trees grow very close together
- 過密 (kamitsu) — overcrowded; excessively dense in population
- 密封 (mippuu) — hermetic sealing; an airtight or watertight closure
- 密室 (misshitsu) — sealed room; locked room; the classic mystery-fiction impossible crime scene
Intimacy and Close Connection
- 親密 (shinmitsu) — intimacy; warmth and closeness in a personal relationship
- 密接 (missetsu) — closely connected; inseparably linked
- 密着 (mitchaku) — close adhesion; sticking tightly to a surface; in journalism, immersive up-close coverage of a subject
Precision and Careful Detail
- 厳密 (genmitsu) — strict, precise, rigorous; the word academic and scientific writing reaches for when exactness matters
- 緻密 (chimitsu) — fine, intricate, painstakingly detailed; used for careful craftsmanship or meticulous intellectual work
- 周密 (shuumitsu) — thorough; meticulous; covering every angle (formal, less common)
Example Sentences
あの二人は親密な関係だ。
Ano futari wa shinmitsu na kankei da.
Those two have an intimate relationship.
秘密を守ることは大切です。
Himitsu wo mamoru koto wa taisetsu desu.
It is important to keep a secret.
この地区は人口が過密だ。
Kono chiku wa jinkou ga kamitsu da.
This area is overpopulated.
その計画は密かに進められた。
Sono keikaku wa hisoka ni susumerareta.
The plan was carried out in secret.
厳密に言えば、それは正確ではない。
Genmitsu ni ieba, sore wa seikaku de wa nai.
Strictly speaking, that is not accurate.
彼は機密情報を外部に漏らした。
Kare wa kimitsu jouhou wo gaibu ni morashita.
He leaked classified information to outside parties.
密輸は重大な犯罪だ。
Mitsuyu wa juudai na hanzai da.
Smuggling is a serious crime.
この事件は密室で起きた。
Kono jiken wa misshitsu de okita.
This incident occurred in a sealed room.
都市の人口密度は年々高くなっている。
Toshi no jinkou mitsudo wa nennen takaku natte iru.
The population density of cities is increasing year by year.
両国は密接な経済関係を築いてきた。
Ryoukoku wa missetsu na keizai kankei wo kizuite kita.
The two countries have built a closely connected economic relationship.
Memory Tip
Picture a mountain (山) hidden under a roof (宀), with certainty (必) sealed at the bottom. A secret underground base, deep inside a mountain, entrance blending into the landscape. Inside: dense rows of equipment, classified files stacked floor to ceiling, operatives working in close quarters. Nothing gets in or out. When you see 密, think of this place — under the hidden roof, within the mountain, secrets are certainly locked away. One image, four meanings: secrecy (the hidden base), density (everything crammed in), closeness (the tight quarters), precision (every detail guarded).