Great deficit in fuel (8)
I believe the answer is:
colossal
'great' is the definition.
(thesaurus)
'deficit in fuel' is the wordplay.
'deficit' becomes 'loss' (I've seen this before).
'in' means one lot of letters goes inside another.
'fuel' becomes 'coal' (coal is a kind of fuel).
'loss' inserted into 'coal' is 'COLOSSAL'.
(Other definitions for colossal that I've seen before include "So locals may be huge" , "Very big" , "Massive" , "Huge, vast" , "Jumbo" .)