Pressure to consume carbon-rich fuel (4)
I believe the answer is:
peat
'fuel' is the definition.
(peat is a kind of fuel)
'pressure to consume' is the wordplay.
'pressure' becomes 'p' (scientific abbreviation).
'to consume' becomes 'eat' (to consume something is to eat it).
'p'+'eat'='PEAT'
'carbon-rich' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for peat that I've seen before include "Decomposed vegetable matter" , "Fuel or compost (but no longer to be used as such!)" , "Form of fuel" , "Fuel from boggy land" , "Partially carbonised vegetable matter used as a fuel when dried" .)