One turning upside down is unchanged? (7)

I believe the answer is:

rotator

I'm a little stuck... Click here to teach me more about this clue!

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

This is the entire clue.

Can you help me to learn more?

(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.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.