発熱（はつねつ、hatsuneつ）
- fever

The Japanese word 発熱 発熱 (hatsunetsu) directly translates to "fever" or "febrile state" in English. It refers to an abnormally high body temperature, often a symptom of illness or infection. It’s a medical term, indicating that someone’s body temperature is elevated above the normal range. It is used to describe the condition itself and not the feeling of being hot.

⚫︎熱があって、発熱しています。 Translation: I have a fever. ⚫︎彼はインフルエンザで発熱しました。 Translation: He developed a fever due to the flu. ⚫︎子供が発熱したので、病院に行きました。 Translation: Because the child had a fever, we went to the hospital.

This word is primarily used in medical contexts, when discussing health with a doctor, or when describing someone's condition to another person. It's a more formal term than simply saying someone is "hot" (atsui). It is often used in medical reports, patient interviews, and health-related conversations.

発熱 is written using the kanji 発 (hatsu - to start, to occur, to leave from) and 熱 (netsu - heat, fever). The reading is はつねつ in hiragana. There is no other way to write this word. The okurigana (the suffix hiragana) is fixed.

There aren't direct synonyms but related phrases include: ⚫︎ 熱がある (netsu ga aru) - to have a fever ⚫︎ 高熱 (kounetsu) - high fever ⚫︎ 微熱 (binetsu) - slight fever (low-grade fever)

There aren’t direct antonyms, but words related to low body temperature or the absence of fever would be: ⚫︎ 平熱 (heinetu) - normal body temperature. ⚫︎ 解熱 (genetsu) - the lowering of a fever; antipyresis.

昨日から発熱があり、今日は学校を休みました。 ・Translation: I've had a fever since yesterday, and I took the day off school today. ・Explanation: This sentence describes the condition of having a fever and its impact on daily activities.

医者は彼の発熱の原因を特定しようとしました。 ・Translation: The doctor tried to identify the cause of his fever. ・Explanation: This sentence describes a doctor's action to understand the cause of the fever.

The kanji 発 means "to start," "to occur," or "to develop." The kanji 熱 means "heat" or "fever." Therefore, 発熱 literally means "the occurrence of heat" or "the development of heat" in the context of the body, indicating a fever. The word accurately describes the state of the body producing excessive heat, which is characteristic of a fever.