熱|ねつnetsu[2]odaka (tail-high)

1. nounheat
   熱ねつによって氷こおりは水みずに変かわる。↗

   Heat turns ice into water.
2. nounfever; temperature
   １０２゜Ｆの熱ねつがあります。↗

   I have a fever of 102 degrees.
3. noun, suffixzeal; passion; enthusiasm; mania; craze; rage
   彼かれは学生がくせい運動うんどう熱ねつに浮うかされている。↗

   He is being carried away by a student movement.

• Synonym発熱はつねつWrittenWritten/formal word for running a fever or for an object giving off heat, as in 「発熱がある」; more formal than 「熱が出る」.
• SynonymヒートCasualLoanword for heat or for a contest heating up, as in 「ヒートアップ」; mostly appears in compounds and is rarely used alone.
• Synonym熱気ねっきNeutralA slightly feverish feeling, as in 「熱っぽい」; read 「ねっき」, it means hot air or the heated excitement of a scene.
• Synonym熱さあつさNeutralThe degree to which an object is hot to the touch, as in 「お湯の熱さ」; focuses on the heat you actually feel.
• Related暑さあつさNeutralRefers to hot weather, as in 「夏の暑さ」; works in both speech and writing, while 「熱」 is physical heat or body temperature.
• Related高温こうおんWrittenWritten/formal word for a high temperature, as in 「高温注意」 or 「高温多湿」; stresses that the temperature reading itself is high.
• Related熱心ねっしんNeutralAdjectival noun for earnest devotion to something, as in 「熱心な学生」; takes the enthusiasm sense of 「熱」 and never refers to temperature.
• Related情熱じょうねつNeutralBurning passion, as in 「情熱を注ぐ」; leans written/formal and is more intense than the enthusiasm sense of 「熱」.
• Related熱意ねついWrittenWritten/formal word for earnest zeal, as in 「熱意が伝わる」; stresses sincerity in getting things done.
• Related熱狂ねっきょうNeutralFrenzied excitement, as in 「観客が熱狂する」; centers on a crowd boiling over.
• Related熱情ねつじょうWrittenWritten/formal word for blazing emotion, as in 「熱情的な演奏」; has a literary flavor.
• Related熱烈ねつれつWrittenWritten/formal word for an ardent manner, as in 「熱烈な歓迎」; stresses the outward show of intensity.
• Related熱血ねっけつNeutralHot-blooded zeal, as in 「熱血教師」; carries a youthful, uplifting color.
• Related熱気ねつけNeutralA slightly feverish feeling, as in 「熱っぽい」; read 「ねっき」, it means hot air or the heated excitement of a scene.
• Related暑気しょきWrittenWritten/formal word for summer heat, as in 「暑気払い」; refers only to the climate.
• Related熱発ねっぱつWrittenMedical term for a fever, found mostly in nursing records; in everyday speech say 「熱が出る」.
• Related熱エネルギーねつエネルギーWrittenPhysics term for thermal energy; emphasizes heat as a form of energy and is used in scientific contexts.
• Antonym冷やひやCasualColloquial word for cold water or unheated sake, or a prefix meaning cold, as in 「お冷や」 and 「冷や飯」; opposes 「熱」 only for concrete things, not heat or fever.
• Antonym冷れいWrittenThe opposite of 「熱」; a written/formal word for cold, mostly in compounds such as 「冷房」 and 「冷水」.
• Antonym寒さむNeutralCold in the chilly, wintry sense, mostly as an element in compounds like 「寒空」 and 「寒気（さむけ）」; opposes 「熱」 in terms of hot and cold.

For physical heat and fever, 「熱」 is the default. Use 「暑さ」 for hot weather and 「熱さ」 for things hot to the touch; say 「発熱」 for fever in formal settings. For enthusiasm pick 「熱心」, 「情熱」 or 「熱意」, and for frenzy 「熱狂」; for cold, turn to 「冷」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 温度おんど差さがある2つの物体ぶったいの間あいだあるいは系けいと周囲しゅういの間あいだで接触せっしょくや放射ほうしゃがあったときに、その温度おんど差さを原因げんいんとして移動いどうする形態けいたいのエネルギー。多おおくの場合ばあいには、物体ぶったいに熱ねつを与あたえれば温度おんどが上あがり、物体ぶったいから熱ねつを取り去とりされば温度おんどが下さがる。
2. 体温たいおん。特とくに、平熱へいねつよりも高たかい状態じょうたい。
3. 物事ものごとに執着しゅうちゃくし、強つよく愛めでる心情しんじょう。情熱じょうねつや熱意ねつい。接尾辞せつびじ的てきにも使用しようされる。