Meaning
At its core, the kanji 膨 (膨) signifies 'to swell,' 'to expand,' 'to bulge,' or 'to inflate.' It describes an increase in volume or size, often resulting from internal pressure or absorption, which causes something to become distended or protrude. This versatile kanji appears in many contexts, ranging from physical phenomena, like balloons inflating or stomachs bloating, to abstract ideas such as expanding budgets or growing expectations.
Etymologically, 膨 is a 形声文字 (keisei moji), or a phono-semantic compound character. It consists of two main parts: a radical and a phonetic component. The left-hand radical, 月 (月), is actually a variant of 肉 (肉), meaning 'flesh' or 'body part,' when it appears on the left side of a kanji as にくづき. This radical often suggests that the kanji’s meaning relates to the body, organs, or physical matter. The right-hand component is 朋 (朋), which typically means 'friend' or 'companion,' but here it functions primarily as the phonetic component, indicating the 'bō' sound. While 朋's original form depicts two identical objects (like two pieces of meat), this combination visually suggests 'flesh' (月) becoming full or expanded, like something pushing outwards. Ultimately, the character signifies a physical or material expansion, becoming full or distended.
With 16 strokes, 膨 is a relatively complex character. As an N1 level kanji, it is not included in the standard 常用漢字 (Jōyō Kanji) list for school grades. This indicates its advanced usage in Japanese.
Readings
On'yomi (音読み) — Chinese-derived readings
The primary 音読み (On'yomi) for 膨 is ボウ (BŌ). This Chinese-derived reading is generally used in compound words, particularly in more formal, technical, or abstract contexts. You'll often find it in scientific, economic, or philosophical discussions concerning expansion or increase.
- 膨張 (bōchō) — expansion, swelling, distension. This is a very common term, used to describe the physical expansion of gases, liquids, or solids, as well as abstract expansion like economic growth.
- 膨大 (bōdai) — enormous, colossal, vast. Describes something that is extremely large in quantity or scale, implying a significant increase beyond normal expectations.
- 膨潤 (bōjun) — swelling (due to absorption of liquid). A more technical term often used in chemistry or material science to describe materials absorbing water and increasing in volume.
Kun'yomi (訓読み) — Native Japanese readings
訓読み (Kun'yomi) readings for 膨 are native Japanese verbs. They are typically used when the kanji appears alone or is followed by 送り仮名 (okurigana). These readings describe direct actions or states of swelling or becoming full, each carrying nuanced differences in usage.
ふくら.む (fukura.mu) — This intransitive verb means 'to swell,' 'to bulge,' 'to expand,' or 'to become full.' It describes a natural or spontaneous increase in volume, applicable to physical objects like balloons, as well as abstract concepts like budgets or expectations.
風船が膨む (fūsen ga fukuramu) — A balloon swells.
期待が膨む (kitai ga fukuramu) — Expectations swell/grow.
予算が膨む (yosan ga fukuramu) — The budget expands.
ふく.れる (fuku.reru) — Also an intransitive verb, ふくれる means 'to swell up,' 'to get bloated,' or 'to get puffed up.' While similar to ふくらむ, it often carries a connotation of something becoming abnormally or undesirably large. It can also imply a negative emotional state, such as pouting or sulking (like puffed-out cheeks in anger), or refer to physical bloating due to gas or indigestion.
パンが膨れる (pan ga fukureru) — Bread rises/swells.
お腹が膨れる (onaka ga fukureru) — One's stomach gets bloated.
頬が膨れる (hoo ga fukureru) — One's cheeks puff out (e.g., from anger or holding air).
ふく.む (fuku.mu) — Though its primary meaning is 'to contain' or 'to include,' ふくむ can also describe a slight swelling or bulging caused by holding something within, like water in one's mouth. However, for the direct sense of 'swelling,' ふくらむ and ふくれる are much more commonly used.
Common Words & Compounds
To truly master 膨, it's crucial to understand how it functions in various compound words and phrases. Below are essential examples, categorized for easier learning:
General Expansion/Growth:
膨張 (bōchō) — expansion, swelling, distension. (例: 熱による金属の膨張 — thermal expansion of metal)
膨大 (bōdai) — enormous, colossal, vast. (例: 膨大な資料 — vast amount of data)
膨む (fukuramu) — to swell, to bulge, to expand (intransitive). (例: 夢が膨む — dreams grow)
膨れる (fukureru) — to swell up, to get bloated (intransitive, often implies undesirable swelling or anger). (例: 胃が膨れる — stomach bloats)
膨らませる (fukuramaseru) — to inflate, to puff out (transitive causative of 膨む). (例: タイヤを膨らませる — to inflate a tire)
Specific States/Conditions:
膨潤 (bōjun) — swelling (due to liquid absorption). (例: 水を吸収して膨潤する — to swell by absorbing water)
膨み (fukurami) — bulge, swelling (noun). (例: 袋の膨み — bulge in a bag)
膨れっ面 (fukurettsura) — a sulky face, a puffed-out face (due to anger). (例: 彼女は膨れっ面になった — She made a sulky face.)
Technical/Economic Terms:
膨張率 (bōchōritsu) — expansion rate. (例: 経済の膨張率 — economic expansion rate)
膨張主義 (bōchō shugi) — expansionism (e.g., political or territorial). (例: 領土を広げる膨張主義 — expansionism to expand territory)
膨張宇宙 (bōchō uchū) — expanding universe. (例: 膨張宇宙論 — theory of the expanding universe)
Example Sentences
風船が空気でどんどん膨んでいく。
Fūsen ga kūki de dondon fukurande iku.
The balloon is swelling more and more with air.
彼の研究は学術的に膨大な影響を与えた。
Kare no kenkyū wa gakujutsuteki ni bōdai na eikyō o ataeta.
His research had an enormous impact academically.
寒暖計の水銀は熱で膨張する。
Kandan-kei no suigin wa netsu de bōchō suru.
The mercury in the thermometer expands with heat.
お腹が空いて、期待で胸が膨んだ。
Onaka ga suite, kitai de mune ga fukuranda.
My stomach was empty, and my heart swelled with anticipation.
子供は思い通りにならず頬を膨らせた。
Kodomo wa omoi dōri ni narazu hoo o fukuramaseta.
The child puffed out their cheeks because things didn't go their way.
乾物は水を含むと膨潤する性質がある。
Kanbutsu wa mizu o fukumu to bōjun suru seishitsu ga aru.
Dried goods have the property of swelling when they absorb water.
会社の事業が急速に膨張している。
Kaisha no jigyō ga kyūsoku ni bōchō shite iru.
The company's business is rapidly expanding.
雨で川の水が溢れんばかりに膨れている。
Ame de kawa no mizu ga afuren bakari ni fukurete iru.
The river water is swollen almost to overflowing due to the rain.
経済の膨張は、新たな雇用を生み出す。
Keizai no bōchō wa, arata na koyō o umidasu.
Economic expansion creates new employment.
予算が予想よりも大きく膨んでしまった。
Yosan ga yosō yori mo ōkiku fukurande shimatta.
The budget swelled much more than expected.
Memory Tip
To help remember 膨, focus on its components. The left part is the にくづき radical (月), a variant of 肉 meaning 'flesh' or 'body part.' The right part is 朋, which typically means 'friend' or 'companion,' but functions here as a phonetic component. For a visual cue, imagine your 'flesh' (月) swelling up so much it resembles 'two' distinct, rounded 'friends' (朋) pressing outward. Think of a belly so full it almost looks like two separate mounds. This exaggerated image of 'flesh' becoming 'bloated' or 'swollen' will help you connect the shape of 膨 to its meaning of 'swell' or 'expand.'