Fuel company with a shortfall finally (4)
I believe the answer is:
coal
'fuel' is the definition.
(coal is a kind of fuel)
'company with a shortfall finally' is the wordplay.
'company' becomes 'co' (abbreviation).
'with' means one lot of letters go next to another.
'finally' indicates one should take the final letters.
The last letter of 'shortfall' is 'l'.
'co'+'a'+'l'='COAL'
(Other definitions for coal that I've seen before include "Char" , "Carbonized vegetable matter" , "slack" , "This consists mainly of carbon" , "Solid fuel" .)