You may well have seen a film on one (5)

I believe the answer is:

spool

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

'film on one' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for spool that I've seen before include "Cylinder for winding film etc" , "On which film is wound" , "Loops around a thread holder" , "Ribbon holder" , "Loops around with reel" .)

I've seen this clue in the Evening Standard.

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