Tidy up room initially left in big mess (9)
I believe the answer is:
imbroglio
'mess' is the definition.
(both can mean a mess or confusion)
'tidy up room initially left in big' is the wordplay.
'tidy up' indicates anagramming the letters (I've seen this in other clues).
'initially' says to take the initial letters.
The first letters of 'left in' is 'li'.
'room'+'li'+'big'='roomlibig'
'roomlibig' with letters rearranged gives 'IMBROGLIO'.
(Other definitions for imbroglio that I've seen before include "Complicated situation" , "Confused and tangled situation" , "Dilemma" , "Jumble" , "quandary" .)