Aggrieved feelings about a source of fuel (4)
I believe the answer is:
peat
'source of fuel' is the definition.
'peat' can be an answer for 'fuel' (peat is a kind of fuel). I'm unsure of the 'source of' bit.
'aggrieved feelings about a' is the wordplay.
'aggrieved feelings' becomes 'pet' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'pet' going around 'a' is 'PEAT'.
Can you help me to learn more?
(Other definitions for peat that I've seen before include "It's used for fuel and in the garden" , "Natural solid fuel" , "Vegetable deposit used as fuel and fertiliser" , "Partially carbonised vegetable matter used as a fuel when dried" , "Bog material" .)