Meaning
The kanji 筒 means tube, cylinder, or pipe — any hollow, elongated, rounded container or conduit. The image behind it is bamboo: a plant that grows in perfectly hollow, cylindrical sections, long used in East Asia as the natural tube. Two of its most common compounds appear in daily Japanese life: 封筒 (envelope) and 水筒 (water bottle). Both are things most Japanese adults handle every week.
The character has two components. The top is 竹 (bamboo, たけかんむり), the semantic radical pointing to the material most associated with tubes in East Asian culture. Bamboo's hollow, segmented structure made it the go-to material for water conduits, containers, and musical instruments for thousands of years. The bottom is 同 (same, together), which served as the phonetic component in the original Chinese. Together: a bamboo object uniform on the inside — the classic tube.
筒 is written with 12 strokes and is a Jōyō kanji (常用漢字) at JLPT N2. It might look specialized at first, but it anchors a tight cluster of high-frequency everyday words that native speakers use constantly.
Readings
On'yomi (音読み) — Chinese-derived readings
The on'yomi reading is トウ (Tō), tracing back to the ancient Chinese pronunciation. It appears mainly in Sino-Japanese compound words (熟語, じゅくご), particularly those related to envelopes and geometric shapes. When 筒 pairs with other kanji of Chinese origin, トウ almost always applies.
- 封筒 (fūtō) — envelope (literally "sealed tube"); the most common word using this kanji
- 円筒 (entō) — cylinder (literally "round tube"); used in mathematics, science, and engineering
- 角筒 (kakutō) — rectangular or square tube; used in packaging and architecture
Kun'yomi (訓読み) — Native Japanese readings
The kun'yomi is つつ (tsutsu), the native Japanese word for a tube or cylinder. It works as a standalone noun and forms part of native compound words. The sound つつ is soft and rounded — tap a piece of bamboo and something close to that sound echoes back. This reading also carries some figurative meanings worth knowing.
- 筒 (tsutsu) — tube, cylinder, pipe (standalone noun)
- 筒先 (tsutsusaki) — nozzle or muzzle; the open tip at the end of a tube
- 筒抜け (tsutsunuke) — leaking out completely, an open secret (lit. "passing clean through a tube"); used when confidential information becomes widely known
- 竹筒 (takezutsu) — bamboo tube; the original archetype of this kanji
Common Words & Compounds
These compounds span daily life, science, and traditional culture. Each is worth learning as a unit.
Everyday Objects:
- 封筒 (fūtō) — envelope; paper envelopes are used constantly in Japanese business and correspondence, more so than in many Western countries
- 水筒 (suitō) — water bottle, canteen; a staple of school life, hiking, and sports in Japan
- 竹筒 (takezutsu) — bamboo tube; used in traditional crafts, garden water features (鹿威し, shishi-odoshi), and Tanabata decorations
- 手筒 (tezutsu) — hand-held firework tube; featured in traditional festivals, especially in Aichi Prefecture
Shape & Geometry:
- 円筒 (entō) — cylinder; a key geometric term in mathematics and physics
- 円筒形 (entōkei) — cylindrical shape; used to describe the form of objects in everyday and technical contexts
- 角筒 (kakutō) — square or rectangular prism tube; used in engineering and packaging design
- 丸筒 (marutsutsu) — round tube; cylindrical roll, such as a poster tube
Figurative & Specialized:
- 筒抜け (tsutsunuke) — information leaking out entirely; an open secret. The image: pour something into one end of a tube and it immediately exits the other — nothing stays inside.
- 筒先 (tsutsusaki) — the tip or mouth of a tube; used for a fire hose nozzle, the muzzle of a gun, or the spout of any tubular device
- 手筒花火 (tezutsu hanabi) — hand-held tube fireworks; participants hold a tube shooting sparks skyward in a dramatic traditional performance
Example Sentences
封筒に切手を貼って、ポストに入れた。
Fūtō ni kitte wo hatte, posuto ni ireta.
I put a stamp on the envelope and dropped it in the mailbox.
山登りをするとき、いつも水筒を持って行く。
Yamanobori wo suru toki, itsumo suitō wo motte iku.
When I go hiking, I always bring a water bottle.
その秘密はもう筒抜けで、みんな知っている。
Sono himitsu wa mō tsutsunuke de, minna shitte iru.
That secret has already leaked out completely — everyone knows about it.
消防士はホースの筒先を火に向けた。
Shōbōshi wa hōsu no tsutsusaki wo hi ni muketa.
The firefighter aimed the nozzle of the hose at the fire.
理科の実験で円筒形の容器を使った。
Rika no jikken de entōkei no yōki wo tsukatta.
We used a cylindrical container in the science experiment.
竹筒から冷たい水を飲んだ。
Takezutsu kara tsumetai mizu wo nonda.
I drank cold water from a bamboo tube.
この封筒の中に大切な書類が入っている。
Kono fūtō no naka ni taisetsu na shorui ga haitte iru.
There are important documents inside this envelope.
手筒花火は愛知県に伝わる伝統的な行事だ。
Tezutsu hanabi wa Aichi-ken ni tsutawaru dentōteki na gyōji da.
Hand-held tube fireworks are a traditional event passed down in Aichi Prefecture.
工場では金属製の円筒を大量に生産している。
Kōjō de wa kinzokusei no entō wo tairyō ni seisan shite iru.
The factory mass-produces cylindrical metal tubes.
Memory Tip
Picture a freshly cut section of bamboo — that is the top of 筒, the 竹 radical. The bottom component is 同, meaning "same" or "uniform." A bamboo object that is uniformly hollow inside. Hold a piece up to the light and see a perfect circle of sky at the other end. That image covers every use of this kanji: 封筒 is a flat paper tube for sealing letters; 水筒 is a modern metal tube for carrying water — just as people once carried water in actual bamboo tubes. Bamboo + uniform inside = tube.