Meaning
The kanji 徹 means to penetrate completely through something — a physical barrier, an entire night, or a task demanding total commitment. Nothing stops halfway. The action continues until the very end without yielding to obstacles, and this unbroken quality is what separates 徹 from ordinary words for effort or completion.
Structurally, 徹 is built around 彳 (gyōninben), the walking-path radical appearing in many kanji connected to movement and travel. The right side pairs elements evoking nurturing (育) with a striking force (攴), together suggesting the image of pushing forward with determination — driving through to the other side rather than stopping short.
Classified as a Jōyō kanji at grade 8 (secondary school level), 徹 belongs to the formal, written register. Written with 15 strokes, its layered structure suits a character whose whole meaning is sustained, deep effort. In modern Japanese it almost always appears in compound words; lone usage and hiragana spellings are essentially absent.
Readings
On'yomi (音読み) — Chinese-derived readings
The only regular on'yomi is テツ (tetsu), which drives virtually every compound featuring this kanji. One phonological point: when テツ directly precedes a syllable beginning with t, k, s, or sh, the ツ becomes っ (a geminate stop). That shift is why 徹底 reads てってい (tettei) rather than てつてい.
- 徹底 (tettei) — thoroughness; the most common compound, appearing daily in phrases like 徹底的に (exhaustively) and 徹底調査 (thorough investigation)
- 徹夜 (tetsuya) — all-nighter; 徹夜する means "to stay up all night," a staple of student and professional vocabulary
- 貫徹 (kantetsu) — carrying something through to full completion; often seen in 初志貫徹 (staying true to one's original intentions)
- 冷徹 (reitetsu) — coldly analytical; describes reasoning or leadership deliberately free from emotional interference
- 透徹 (tōtetsu) — penetrating clarity; logic or vision that cuts cleanly through complexity without distortion
Kun'yomi (訓読み) — Native Japanese readings
The kun'yomi とお・す (tōsu) surfaces mainly in set phrases and literary texts. Written 徹す, it functions as a transitive verb: to make something pass entirely through, or to see something all the way to the end. The everyday verb 通す (same reading, different kanji) handles ordinary "passing through"; choosing 徹す marks a stronger, unbreakable resolve — nothing will interrupt this before it finishes.
- 夜を徹して (yo wo tōshite) — throughout the night, working without rest; a set phrase found in both spoken and written registers
- 徹し (tōshi) — the nominalized form, the act of seeing something completely through
Recognize this kun'yomi in set phrases and literary passages even if active production opportunities are rare.
Common Words & Compounds
Every compound below ties back to completeness — whether of effort, insight, or time stretching unbroken through an entire night.
Everyday vocabulary:
- 徹底 (tettei) — thoroughness; collocates with 徹底的に (exhaustively, with full rigor) and 徹底調査 (thorough investigation)
- 徹夜 (tetsuya) — all-nighter; 徹夜する means "to stay up all night"
- 徹底的 (tetteiteki) — thorough, exhaustive; the adjectival form of 徹底, used predicatively and attributively
Formal and literary vocabulary:
- 貫徹 (kantetsu) — carrying through to full completion; appears in 意志貫徹 (steadfast determination) and 初志貫徹 (staying true to one's original intentions)
- 冷徹 (reitetsu) — coolly rational; used for leaders, judges, or analysts who reason without sentimentality
- 透徹 (tōtetsu) — penetrating clarity; for logic, artistic vision, or understanding that is sharp and unclouded
- 徹する (tessuru) — to penetrate, to commit fully; as in 悪役に徹する (to throw oneself completely into a villain role)
Advanced and specialized vocabulary:
- 徹頭徹尾 (tettō tetsubi) — from beginning to end, through and through; a yojijukugo expressing total consistency without exception
- 徹宵 (tesshō) — throughout the entire night; a formal, literary alternative to 徹夜
- 徹底抗戦 (tettei kōsen) — fighting to the last, total resistance; common in historical, political, and sports journalism
Example Sentences
彼女は試験の前に徹夜で勉強した。
Kanojo wa shiken no mae ni tetsuya de benkyō shita.
She studied all night before the exam.
この問題は徹底的に調査する必要がある。
Kono mondai wa tetteiteki ni chōsa suru hitsuyō ga aru.
This problem needs to be investigated thoroughly.
彼は最後まで自分の意志を貫徹した。
Kare wa saigo made jibun no ishi wo kantetsu shita.
He carried his will through to the very end.
冷徹な判断力が優れたリーダーには求められる。
Reitetsu na handanryoku ga sugureta rīdā ni wa motomerareru.
A cool, analytical judgment is required of an excellent leader.
彼は徹頭徹尾正直な人間だ。
Kare wa tettō tetsubi shōjiki na ningen da.
He is an honest person through and through.
救助隊は夜を徹して行方不明者を探し続けた。
Kyūjotai wa yo wo tōshite yukuefumeisha wo sagashi tsuzuketa.
The rescue team continued searching for the missing person throughout the night.
社長は工場全体に徹底した品質管理を指示した。
Shachō wa kōjō zentai ni tettei shita hinshitsu kanri wo shiji shita.
The president ordered thorough quality control throughout the entire factory.
透徹した論理で、彼女はすべての反論を退けた。
Tōtetsu shita ronri de, kanojo wa subete no hanron wo shirizoketa.
With penetrating logic, she dismissed every counterargument.
彼は悪役に徹して、観客を驚かせた。
Kare wa akuyaku ni tesshite, kankyaku wo odorokaseta.
He committed fully to the villain role and astonished the audience.
Memory Tip
Picture a lone traveler — the 彳 walking radical on the left — who vows to reach the destination no matter what. Night falls. The traveler keeps walking. Midnight passes. Still walking. Dawn arrives, and the traveler finally stops, not having rested once. That image of unbroken movement through an entire night maps directly onto the two most important compounds: 徹夜 (tetsuya, literally "penetrating through the night") and 徹底 (tettei, literally "penetrating to the very bottom").
The character's 15 strokes mirror the sustained, layered effort its meaning demands — no shortcut, no stopping short.