Debacle if backing a second business (6)
I believe the answer is:
fiasco
'debacle' is the definition.
(synonyms)
'if backing a second business' is the wordplay.
'backing' is a reversal indicator.
'a second' becomes 'as' (I've seen this in other clues).
'business' becomes 'co'.
'if' back-to-front is 'fi'.
'fi'+'as'+'co'='FIASCO'
(Other definitions for fiasco that I've seen before include "washout" , "Sudden total disaster" , "Complete disaster" , "Ridiculous and total failure" , "A debacle, complete mess" .)