With the swap in train, Ed returned (5-2)
I believe the answer is:
trade-in
'with the swap' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'in train ed returned' is the wordplay.
'in' indicates putting letters inside.
'returned' says the letters should be written in reverse.
'ed' written backwards gives 'de'.
'train' enclosing 'de' is 'TRADE-IN'.
Can you help me to learn more?
(Other definitions for trade-in that I've seen before include "Older article used in part payment to retailer" , "Something used in part exchange" , "Article used in part payment for another" , "Trained (anag.)" , "Article used in part-exchange" .)