Burn chunk of peat or charcoal (5)
I believe the answer is:
torch
'burn' is the definition.
(torching is a kind of burning)
'chunk of peat or charcoal' is the wordplay.
'chunk of' indicates a hidden word.
'TORCH' can be found hidden inside 'peat or charcoal'.
(Other definitions for torch that I've seen before include "Link" , "Set fire to - hand-held light" , "may get one glowing" , "Source of light" , "Flashlight" .)