暑い
あつい
atsui
= hot (weather / air temperature)
暑い (atsui) is how you say it’s hot when you mean the weather — a sweltering summer day, a stuffy room, the heat of the air around you. It’s one of the first words you’ll actually use in Japan, and one that hides a trio of look-alike homophones worth sorting out.
暑い describes hot air or hot weather: 今日は暑い (it’s hot today), 暑い夏 (a hot summer), 部屋が暑い (the room is stuffy/hot). It refers to the temperature of your surroundings, not of an object you touch, and its natural opposite is 寒い (samui), ‘cold’ as in cold weather.
The crucial thing for learners is that three different kanji all read atsui. 暑い is hot weather; 熱い is hot to the touch (熱いお茶, hot tea; 熱いお風呂, a hot bath) and, figuratively, passionate (熱い議論, a heated debate); 厚い means thick (厚い本, a thick book). They sound identical, so only the kanji and context distinguish them — a bowl of ramen is 熱い, a July afternoon is 暑い.
A very useful relative is 蒸し暑い (mushiatsui), ‘hot and humid / muggy’, which combines 蒸す (to steam) with 暑い. Given Japan’s sticky summers, you will hear 蒸し暑い constantly. Note also the parallel split on the cold side: weather that is cold is 寒い, but an object that is cold to the touch is 冷たい (tsumetai) — the same ‘surroundings versus object’ logic that separates 暑い from 熱い.
Match 暑い to the weather and 熱い to objects. Coffee is 熱い, not 暑い; a heatwave is 暑い, not 熱い. Getting this backwards is one of the most common learner mix-ups because the sound is the same.
Pair 暑い with 寒い, not 冷たい. When contrasting weather, 暑い and 寒い go together; 冷たい is for touching something cold like ice or a drink.
Reach for 蒸し暑い in summer. Plain 暑い states it’s hot, but Japan’s humidity usually calls for 蒸し暑い (‘muggy’), which sounds far more natural to locals during the rainy and midsummer seasons.
Everyday use
今日は本当に暑いから、水をたくさん飲んでね。
Kyou wa hontou ni atsui kara, mizu wo takusan nonde ne.
It’s really hot today, so drink plenty of water.
Casual / Social Media
日本の夏は蒸し暑くて、外に出るのがつらい。
Nihon no natsu wa mushiatsukute, soto ni deru no ga tsurai.
Japanese summers are so muggy that going outside is rough.
Formal / Cultural context
室内が暑いので、エアコンをつけてもよろしいですか。
Shitsunai ga atsui node, eakon wo tsukete mo yoroshii desu ka.
It’s hot inside, so may I turn on the air conditioner?
Japan’s summers make 暑い an unavoidable part of daily talk. The rainy season gives way to a famously 蒸し暑い (muggy) midsummer, and weather reports warn of 猛暑 (moushou, fierce heat) and 猛暑日 (days over 35°C). Alongside them come constant 熱中症 (necchuushou, heatstroke) alerts urging people to hydrate and rest, so the vocabulary of heat is tied closely to public health.
Because the heat is so relentless, Japan has a rich culture of coping with it. Traditions like 打ち水 (uchimizu, sprinkling water on pavements to cool the air), hanging 風鈴 (wind chimes) for a psychologically cooler sound, and eating かき氷 (shaved ice) are all seasonal responses to being 暑い, blending practicality with a certain summer aesthetic.
The heat even shapes etiquette and letters. Late-summer heat that lingers past the calendar’s start of autumn is 残暑 (zansho), and people send 残暑見舞い — greeting cards checking on others’ well-being during the remaining heat. That such a specific word and custom exist shows how central the experience of being 暑い is to the rhythm of the Japanese year.