Pairs in middle of slow lane advance (4)
I believe the answer is:
loan
'advance' is the definition.
(an advance is a loan)
'pairs in middle of slow lane' is the wordplay.
'pairs' becomes 'copulates' ('copulate' can be a synonym of 'pair').
'in middle' means to look at the middle letters.
'of' becomes 'o''.
'slow lane' becomes 'an' (I can't justify this - if you can you should believe this answer much more).
The centre of 'copulates' is 'l'.
'l'+'o'+'an'='LOAN'
Can you help me to learn more?
(Other definitions for loan that I've seen before include "Act of lending" , "temporary payment" , "It's given temporarily" , "Credit" , "One acquired temporarily" .)