Something for smoking jacket (6)

I believe the answer is:

reefer

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'jacket' is the definition.
(I know that reefer is a type of jacket)

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

Can you help me to learn more?

(Other definitions for reefer that I've seen before include "Kind of jacket - joint" , "A wool jacket; a spliff" , "courses may be reduced by one" , "J" , "Nautical jacket" .)

I've seen this clue in The Independent and The Telegraph.

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