Small amount of coal? It’s a lot of fuel (3)
I believe the answer is:
pea
'small amount of coal?' is the definition.
I can't tell whether this defines the answer.
'a lot of fuel' is the wordplay.
'a lot of' means to remove the last letter (most of the word but not all of it).
'fuel' becomes 'peat' (peat is a kind of fuel).
'peat' with its last letter taken away is 'PEA'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for pea that I've seen before include "It may climb frame" , "veg" , "Seed eaten as vegetable" , "12 in a pod" , "The plant is a strange ape" .)