adverb
in or into a position in which the top of sth is where the bottom is normally found and the bottom is where the top is normally found :
The canoe floated upside down on the lake.
OPP right side up
► ˌupside ˈdown adjective [ not usually before noun ]:
The painting looks like it's upside down to me.
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IDIOMS
- turn sth upside down
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WORD ORIGIN
Middle English : originally up so down , perhaps in the sense up as if down .