Free fairground attraction ejects last in line (3)

I believe the answer is:

rid

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'free' is the definition.
(to be free of something is to be rid of it)

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

Can you help me to learn more?

(Other definitions for rid that I've seen before include "Clear, remove" , "Free from something unpleasant" , "Free (someone of something unwanted)" , "Free, deliver, clear" , "Free, relieve" .)

I've seen this clue in The Times.

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