Large chunk of his labours (4)
I believe the answer is:
slab
'large chunk' is the definition.
(I've seen this in another clue)
'of his labours' is the wordplay.
'of' says the answer is hidden in the clue.
'SLAB' can be found hidden inside 'his labours'.
(Other definitions for slab that I've seen before include "Large block of stone or concrete" , "Broad, thick piece of wood, stone" , "24 tinnies [STRINE] < in a wooden hut [STRINE]" , "Thick piece of something" , "Large thick slice (of cake etc)" .)