The head slab of wood (5)
I believe the answer is:
block
This could be a double definition.
'the head' is the first definition.
(a barber's block is a head for storing a wig)
'slab of wood' is the second definition.
'block' can be an answer for 'slab' (thesaurus). I'm not certain of the 'of wood' bit.
Can you help me to learn more?
(Other definitions for block that I've seen before include "Cube" , "City area; prevent flow" , "Jam" , "Solid shape; prevent" , "Obstruct" .)