筒
つつ · tsutsu · JLPT N1 · noun
tube
Radical 竹 means bamboo: hollow bamboo stalks were the original tubes and pipes
The 竹 radical marks bamboo, since hollow bamboo stalks were the first pipes. Related word: 水筒 (suitou), a water bottle, is a tube you carry.
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.