Meaning
The kanji 核 means 'nucleus,' 'core,' or 'kernel.' It signifies the central, essential, or innermost part of something, encompassing both physical objects and abstract concepts. Literally, it can refer to the hard pit or seed inside a fruit, such as a peach or plum. Figuratively, it denotes the most vital element of an idea, a group, or a system.
Its etymological roots clearly show this core meaning. 核 is a phono-semantic compound. This means it combines 木, a semantic component (radical) suggesting 'tree' or 'wood,' with 亥, a phonetic component that provides the 'kaku' sound. The radical 木 on the left naturally links the kanji to plants, fruits, and their seeds or kernels. The right component, 亥, also means 'boar' or 'pig.' From this origin, the image of a 'kernel' or 'pit' from a 'tree' or 'plant' is deeply embedded, later expanding to signify 'core' or 'nucleus' in a broader, more abstract sense.
This kanji has 10 strokes. While not assigned a specific elementary school grade level, it is a Jōyō kanji frequently encountered in secondary education. It's also a common and important part of JLPT N1 vocabulary.
Readings
On'yomi (音読み) — Chinese-derived readings
The primary and most common on'yomi for 核 is カク (Kaku).
カク (Kaku)
This reading is widely used across many fields, especially in scientific, political, and general terms where 'nucleus,' 'core,' or 'kernel' is implied. It's the primary reading for most compound words using this kanji.
- 核 (kaku) — nucleus; kernel; core (often used as a prefix)
- 原子核 (genshikaku) — atomic nucleus
物理学者は原子核の構造を研究しています。
- 細胞核 (saibōkaku) — cell nucleus
生物学では、細胞核が遺伝情報を格納しています。
- 核心 (kakushin) — core; heart; gist
その議論の核心は、人権についてでした。
Kun'yomi (訓読み) — Native Japanese readings
While 核 is predominantly used with its on'yomi, it does have one specific kun'yomi.
さね (sane)
This reading, さね (sane), is less common for the standalone kanji 核 in general usage. However, it specifically refers to the 'kernel' or 'pit' of a fruit. In this context, it means the hard part inside a fruit that contains the seed, like a peach or plum pit. When referring to a fruit pit, it's typically written as 核.
- 核 (sane) — kernel; pit (of a fruit)
- 梅の核 (ume no sane) — plum pit
梅の核を取り除いてからジャムを作ります。
- 桃の核 (momo no sane) — peach pit
桃の核はとても硬いです。
Common Words & Compounds
The kanji 核 appears in many important compound words, particularly in scientific, technological, and sociological fields. Learning these compounds is highly beneficial for N1 students.
General & Scientific Terms:
核 (kaku) — nucleus; kernel; core (often as a prefix)
原子核 (genshikaku) — atomic nucleus
細胞核 (saibōkaku) — cell nucleus
核反応 (kakuhannō) — nuclear reaction
核融合 (kakuyūgō) — nuclear fusion (e.g., in the sun)
核分裂 (kakubunretsu) — nuclear fission (e.g., in reactors)
Abstract & Sociological Terms:
核心 (kakushin) — core; heart; gist; crucial point
会議の核心に迫る。
- 中核 (chūkaku) — core; nucleus; central figure/element
そのチームの中核メンバー。
核家族 (kakukazoku) — nuclear family (parents and children only)
核となる (kaku to naru) — to be the core/nucleus of; to be central to この技術がプロジェクトの核となるでしょう。
Military & Political Terms:
核兵器 (kakuheiki) — nuclear weapon
核不拡散 (kakufukakusan) — nuclear non-proliferation
核実験 (kakujikken) — nuclear test
Example Sentences
この問題の核心を理解することが重要です。
Kono mondai no kakushin o rikai suru koto ga jūyō desu.
It is important to understand the core of this problem.
原子核は陽子と中性子でできています。
Genshikaku wa yōshi to chūseishi de dekite imasu.
An atomic nucleus is made up of protons and neutrons.
彼の話の核心部分は非常に興味深かった。
Kare no hanashi no kakushin bubun wa hijō ni kyōmibukakatta.
The core part of his story was very interesting.
多くの国が核兵器の廃絶を求めています。
Ōku no kuni ga kakuheiki no haizetsu o motomete imasu.
Many countries are calling for the abolition of nuclear weapons.
現代社会では核家族が一般的になりつつあります。
Gendai shakai de wa kakukazoku ga ippan-teki ni nari tsutsu arimasu.
The nuclear family is becoming common in modern society.
この研究プロジェクトの中核は新しい素材の開発です。
Kono kenkyū purojekuto no chūkaku wa atarashii sozai no kaihatsu desu.
The core of this research project is the development of new materials.
細胞の核は生命活動に不可欠です。
Saibō no kaku wa seimei katsudō ni fukaketsu desu.
The cell's nucleus is indispensable for life activities.
それは問題を解決するための核となるアイデアだ。
Sore wa mondai o kaiketsu suru tame no kaku to naru aidea da.
That is the core idea for solving the problem.
古い梅の核から新しい芽が出た。
Furui ume no sane kara atarashii me ga deta.
A new sprout emerged from the kernel of an old plum.
Memory Tip
To remember 核, think of its components: 木 (tree) and 亥 (boar/pig). Imagine a hungry boar (亥) eagerly digging under a tree (木) to find the delicious 'kernel' or 'core' of a nut or fruit buried beneath the roots. The sound 'Kaku' could be like the sharp 'crack' sound of the boar breaking open a hard nut to get to its core. This visual story helps connect the 'tree' radical to the meaning of a 'kernel' or 'pit' from a plant. The 'boar' component offers a memorable link to the sound and the idea of getting to the 'core' of something.