病気
びょうき
byouki
= illness; sickness; disease
病気 (byouki) is the everyday Japanese word for illness or sickness — but it pulls double duty as casual slang for someone who is “nuts” or obsessively fixated on something, giving this single word a surprisingly wide emotional range.
In its primary sense, 病気 refers to any illness, sickness, or disease: 病気になる (byouki ni naru) means “to get sick,” and 病気で休む (byouki de yasumu) means “to take time off due to illness.” It covers everything from a common cold to a serious condition, making it the go-to general term a doctor or employer would understand.
Colloquially, あいつ病気だ (aitsu byouki da) — literally “that person is sick” — is used half-jokingly to describe someone with an extreme obsession or unusual fixation, such as a hardcore fan who spends every yen on merchandise. This slang use is informal and affectionate among friends, but can come across as rude with people you don’t know well.
病気 differs from related words in important ways: 病 (yamai) is a more literary or poetic term for the same concept; けが (kega) refers specifically to a physical injury rather than an illness; and 風邪 (kaze) is narrowly a cold or flu.
Keep three terms distinct: 病気 (byouki) is the broad term for any illness; けが (kega) is a physical injury like a sprain or cut; 風邪 (kaze) is specifically a cold or flu. When filling out a leave-of-absence form or telling your boss you’re unwell, 病気 is always the right choice.
Also note the kanji in related words: 病院 (byouin, hospital) and 医院 (iin, small clinic) both relate to medical care but differ in scale and formality — 病院 is the larger institution sharing the 病 kanji.
For the slang sense, stick to close friends or online contexts where the playful intent is obvious; in a workplace or with strangers, calling someone 病気 for their hobby would be genuinely offensive.
病 is built from 疒 (yamai-dare), the sickness radical depicting a person leaning weakly against a surface, combined with 丙 (hei), which contributes the sound. 気 (ki) represents life energy or vital spirit — the same concept as qi in Chinese medicine. Together, 病気 literally conveys the idea of “sickened energy” or “weakened spirit,” directly reflecting the traditional East Asian understanding that illness is a disruption of the body’s natural vital force.
Everyday use
熱があって会社を休みます。病気です。
Netsu ga atte kaisha wo yasumimasu. Byouki desu.
I have a fever and will be absent from work. I’m sick.
Casual / Social Media
あの人、毎月ガンプラに五万円も使うって。もう病気だよ。
Ano hito, maitsuki Gunpura ni goman-en mo tsukau tte. Mou byouki da yo.
I heard that person spends 50,000 yen on Gunpla every month. They’re absolutely obsessed.
Formal / Cultural context
先生、最近ずっと疲れやすくて、何か病気でしょうか。
Sensei, saikin zutto tsukare yasukute, nanika byouki deshou ka.
Doctor, I’ve been feeling fatigued lately — could something be wrong with me?
In Japanese workplaces, 体調管理 (taichou kanri) — managing one’s physical condition — is treated as a professional responsibility rather than a purely personal matter. Showing up healthy and not spreading illness to colleagues is an unspoken expectation, which is why phrases like 病気で休む carry a certain social weight. When a colleague does fall ill, expressions of concern (お大事に, odaiji ni — “please take care”) function as a scripted social ritual that acknowledges both the person’s condition and their commitment to returning promptly.
The concept of 気 (ki) as vital energy underpins how illness is intuitively framed in Japanese. Traditional East Asian medicine viewed health as the free circulation of ki through the body, and disruption of that flow as the root of 病気. While modern Japanese medicine is fully Western in practice, this conceptual heritage lingers in everyday idioms: 気分が悪い (kibun ga warui, feeling unwell) and 元気 (genki, good health/energy) both draw on the same character, quietly connecting daily conversation to centuries of medical philosophy.