Lift a chunk of wood (5)
I believe the answer is:
balsa
'wood' is the definition.
(balsa wood is a kind of wood)
'lift a chunk' is the wordplay.
'lift' says the letters should be written backwards (I've seen 'lifting' mean this).
'chunk' becomes 'slab' (I have seen 'Chunk of wood' mean 'slab' so perhaps 'chunk' could also mean 'slab').
'a'+'slab'='aslab'
'aslab' written backwards gives 'BALSA'.
'of' acts as a link.
(Other definitions for balsa that I've seen before include "South American tree" , "Raft-making S American corkwood" , "A slab (anag.)" , "Strong, light wood" , "lightweight boat-builder" .)