水筒
すいとう · suitou · JLPT N2 · noun
water bottle
水 (water) + 筒 (tube, cylinder): a tube that holds water, i.e. a water bottle or canteen
The 筒 (tou) in 水筒 names a hollow cylinder, like a bamboo tube or pipe. Put water in that tube and you have a canteen or flask. The same 筒 appears in 封筒 (envelope).
水 — pictograph of flowing water
水 is a pictograph depicting a stream of flowing water, with the central line representing the main current and the side strokes showing splashing droplets or ripples. In oracle bone script it was drawn even more clearly as a wavy vertical line with branches. It retains its original meaning of 'water' and also serves as a radical, often appearing in the compressed form 氵.
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.