Old trousers that go round on the carousel (4)

I believe the answer is:

bags

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'old trousers' is the definition.
'bags' can be an answer for 'trousers' (informal term for trousers, Oxford bags). I am unsure of the 'old' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for bags that I've seen before include "Lots of" , "Containers for carrying, informally plenty" , "a great deal" , "Gets" , "Criticises" .)

I've seen this clue in The Times.

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