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pipe; tube; cylinder
gun barrel
gun; cannon
well lining; well curb
「筒」 has other readings with different meanings.
紙を丸めて筒状にして望遠鏡の真似をした。
I rolled up paper into a tube and pretended it was a telescope.
竹の筒に季節の花を生けて飾った。
I arranged flowers in a bamboo tube as decoration.
ポスターは筒に入れて持ち運ぶと便利だ。
It is convenient to carry posters in a tube.