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lattice
counter for large bundles (e.g. 10 sheafs of rice, 200 sheets of calligraphy paper, 20 whistling arrows, 100 fish)
handbreadth (unit for measuring the length of arrows)
「束」 has other readings with different meanings.
母の日に花を一束買ってプレゼントしました。
I bought a bunch of flowers.
この店では新鮮な野菜三束で百円になります。
Three bunches of vegetables for 100 yen.
数学の授業で束の概念を学んだ。
We learned the concept of a lattice in math class.