A block turned in wood (5)
I believe the answer is:
balsa
'wood' is the definition.
(balsa is a kind of wood)
'a block turned' is the wordplay.
'block' becomes 'slab' (slab is a kind of block).
'turned' is a reversal indicator.
'a'+'slab'='aslab'
'aslab' reversed gives 'BALSA'.
'in' is the link.
(Other definitions for balsa that I've seen before include "South American tree" , "Very lightweight wood from tropical tree" , "Strong, light wood" , "Tree with light soft wood" , "A slab (anag.)" .)