Drop in business after Christmas time (7)
I believe the answer is:
decline
'drop' is the definition.
(declining is a kind of dropping)
'business after christmas time' is the wordplay.
'business' becomes 'line' (line is a kind of business).
'after' means one lot of letters go next to another.
'christmas time' becomes 'dec' (I can't explain this - if you can you should give a lot more credence to this answer).
'line' put after 'dec' is 'DECLINE'.
'in' is the link.
Can you help me to learn more?
(Other definitions for decline that I've seen before include "Fade" , "Start to fail" , "Dwindle" , "Refuse - dip" , "The classics student must often" .)