封筒
ふうとう · fuutou · JLPT N5 · noun
envelope
✉️ 封筒 = seal (封) + tube (筒): a sealed tube for letters
封 means to seal or close up, and 筒 means a tube or cylinder. Letters were once rolled and sealed inside a tube, so a sealed tube became the word for envelope. Sound hook: fuutou — you go foo-toe the mailbox to send it.
封 — earth 土 doubled (圭) + inch 寸 (hand)
Originally a pictograph of a hand planting a sapling on a mound of earth, marking a boundary. From this came the meaning of granting fiefs to nobles, then sealing or closing off territory. The modern senses 'to seal' and 'envelope' both stem from this idea of enclosing.
筒 — bamboo radical 竹 + tóng 同 (phonetic)
A semantic-phonetic compound. The bamboo radical 竹 on top signals the meaning, since early tubes and containers were made from hollow bamboo segments, while 同 below supplies the sound 'tóng'. The original sense was a bamboo tube, later broadened to any cylindrical container like a bucket or canister.