Meaning
剤 (ざい) means medicine, drug, pharmaceutical preparation, or chemical agent. It appears almost exclusively in medical, pharmaceutical, and chemical contexts — from the laundry detergent label to a prescription slip at a Japanese hospital. Scan any pharmacy shelf in Japan and 剤 shows up on nearly every box; it is equally common on household cleaning products and agricultural packaging.
Etymologically, 剤 combines two components. The left is a simplified form of 斉 (せい), which originally depicted grain stalks growing in even rows — evoking uniformity, balance, and exact adjustment. The right is 刂, the side-form of the knife radical 刀 (とう). Together they picture an ancient apothecary cutting and measuring ingredients with a blade to produce a perfectly balanced medicinal formula: something carefully prepared, nothing left to chance.
With 10 strokes, 剤 sits on the official Jōyō kanji (常用漢字) list at the secondary-school level — a sign of its technical, specialized character. The traditional Chinese form is 劑, a heavier 18 strokes. Japan trimmed that to 10 during postwar kanji reform without changing the meaning. Knowing 剤 gives you a key to vocabulary spanning healthcare, chemistry, and everyday consumer products.
Readings
On'yomi (音読み) — Chinese-derived readings
剤 has exactly one On'yomi reading: ザイ (ZAI). Unlike many kanji that carry multiple Chinese-derived pronunciations, this one stays simple. The ZAI sound traces back to the Middle Chinese pronunciation of 齊/劑 — something close to dzɛj in ancient phonology. Over centuries of cultural exchange, that sound settled into the modern ザイ form.
ザイ appears in every compound that uses this kanji, without exception. Whether you are at a pharmacy, reading a cleaning product label at the supermarket, or studying chemistry, the reading is always ザイ.
Core examples using the ザイ reading:
- 薬剤 (yakuzai) — pharmaceutical drug, medicine
- 洗剤 (senzai) — detergent, cleaning agent
- 錠剤 (jōzai) — tablet, pill form of medicine
Kun'yomi (訓読み) — Native Japanese readings
No kun'yomi reading exists for 剤. That is typical of technical kanji imported into Japan alongside their Chinese pronunciation — particularly those arriving through medical and scholarly texts. The concept of a carefully prepared pharmaceutical agent came to Japan through Chinese medicine, so speakers adopted the character and its Chinese-derived reading as a unit. No native Japanese word was ever mapped onto it.
For reading, 剤 is one of the simpler N1 kanji. Focus on the compound words — the reading never varies from ザイ.
Common Words & Compounds
Learning 剤 opens up a broad family of vocabulary. These compounds turn up on medicine packaging, safety labels, public health articles, and JLPT reading passages.
Medical & Pharmaceutical:
- 薬剤 (yakuzai) — pharmaceutical drug, medicine compound
- 薬剤師 (yakuzaishi) — pharmacist (literally "pharmaceutical agent master")
- 錠剤 (jōzai) — tablet, solid pill form of medicine
- 鎮痛剤 (chintsūzai) — painkiller, analgesic
- 消毒剤 (shōdokuzai) — disinfectant, antiseptic agent
- 催眠剤 (saiminzai) — sleeping pill, soporific
- 栄養剤 (eiyōzai) — nutritional supplement, vitamin preparation
- 胃腸剤 (ichōzai) — digestive medicine, gastrointestinal remedy
Household & Cleaning:
- 洗剤 (senzai) — detergent, cleaning agent
- 漂白剤 (hyōhakuzai) — bleach, whitening agent
- 防腐剤 (bōfuzai) — preservative, antiseptic preserving agent
- 接着剤 (setchakuzai) — adhesive, glue
Agriculture & Chemistry:
- 除草剤 (josōzai) — herbicide, weed killer
- 殺虫剤 (satchūzai) — insecticide, pesticide
- 防虫剤 (bōchūzai) — insect repellent, moth-proofing agent
- 溶剤 (yōzai) — solvent (chemistry)
Example Sentences
この薬剤は一日三回飲んでください。
Kono yakuzai wa ichinichi sankai nonde kudasai.
Please take this medicine three times a day.
洗剤を使って食器を洗います。
Senzai wo tsukatte shokki wo araimasu.
I wash the dishes using detergent.
薬剤師に相談してから薬を買いました。
Yakuzaishi ni sōdan shite kara kusuri wo kaimashita.
I bought the medicine after consulting with a pharmacist.
錠剤は水と一緒に飲んでください。
Jōzai wa mizu to issho ni nonde kudasai.
Please take the tablet together with water.
この食品には防腐剤が入っていません。
Kono shokuhin ni wa bōfuzai ga haitte imasen.
This food product contains no preservatives.
鎮痛剤を飲んだら、頭痛がよくなりました。
Chintsūzai wo nondara, zutsū ga yoku narimashita.
After taking the painkiller, my headache got better.
除草剤をまくと雑草が枯れます。
Josōzai wo maku to zassō ga karemasu.
If you spray herbicide, the weeds will wither and die.
接着剤でプラモデルを組み立てます。
Setchakuzai de puramaderu wo kumitatemasu.
I assemble the plastic model kit using adhesive.
消毒剤を傷口につけてください。
Shōdokuzai wo kizuguchi ni tsukete kudasai.
Please apply disinfectant to the wound.
漂白剤を使うと服が白くなります。
Hyōhakuzai wo tsukau to fuku ga shiroku narimasu.
Using bleach makes your clothes turn white.
Memory Tip
Try this: picture a scientist named Zai in a pristine laboratory. He holds a knife in one hand — that is the 刂 radical on the right — not to harm anyone, but to slice and measure ingredients with total precision. Everything on his bench is perfectly equal and uniform (the 斉 component on the left), because medicine demands exact proportions. Every milligram counts; every cut is deliberate. Next time you spot 剤 on a product label, picture Zai at his bench, knife in hand. That image of measured, exacting preparation is the heart of this kanji.