Failing business at the end of last month (7)
I believe the answer is:
decline
'failing' is the definition.
(thesaurus)
'business at the end of last month' is the wordplay.
'business' becomes 'line' (as in someone's line of work).
'at the end of' is a charade indicator (letters next to each other) (some letters go at the end of others).
'last month' becomes 'dec' (December, last month of the year).
'line' after 'dec' is 'DECLINE'.
(Other definitions for decline that I've seen before include "Start to fail" , "Diminish; deteriorate" , "Refuse - dip" , "Refuse - to go down" , "Downturn - turn down" .)