Transfer energy inside a conveyance (6)

I believe the answer is:

reefer

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But I can't explain it at all! Could you help me understand?

(Other definitions for reefer that I've seen before include "Kind of jacket - joint" , "Something designed for smoking" , "cold vehicle" , "Joint; spliff" , "packed with cannabis?" .)

I've seen this clue in The Hindu.

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