Brought up a slab of wood (5)
I believe the answer is:
balsa
'wood' is the definition.
(type of wood)
'brought up a slab' is the wordplay.
'brought up' says the letters should be written backwards (in a down clue, letters go up).
'a'+'slab'='aslab'
'aslab' backwards is 'BALSA'.
'of' acts as a link.
(Other definitions for balsa that I've seen before include "Wood used by model makers" , "Tropical American tree" , "Very lightweight wood from tropical tree" , "Strong, light wood" , "A slab (anag.)" .)