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top and bottom; high and low; above and below; upper and lower ends; up and down
going up and down; rising and falling; fluctuating
going and coming back
upper and lower classes; ruler and ruled; the government and the people
first and second volumes
top and bottom; two-piece (outfit)
「上下」 has other readings with different meanings.
棚の上下を入れ替えた。
I swapped the top and bottom shelves.
体温が上下して体調が安定しない。
My body temperature fluctuates and my health isn't stable.
エレベーターが上下に動いている。
The elevator is moving up and down.