Large depreciation in fuel (8)
I believe the answer is:
colossal
'large' is the definition.
(similar in meaning)
'depreciation in fuel' is the wordplay.
'depreciation' becomes 'loss' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'fuel' becomes 'coal' (coal is a kind of fuel).
'loss' inserted into 'coal' is 'COLOSSAL'.
Can you help me to learn more?
(Other definitions for colossal that I've seen before include "Great" , "Jumbo" , "Massive" , "Mammoth" , "Stupendous" .)