One turning upside down is unchanged? (7)

I believe the answer is:

rotator

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'one turning upside down is unchanged?' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

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(Other definitions for rotator that I've seen before include "One palindromic turner ..." , "Device that spins" , "Something turning" , "this one is for turning" , "One goes round" .)

I've seen this clue in The Independent.

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