Worker starts to chop hard wood (5)
I believe the answer is:
beech
'wood' is the definition.
(I know that beech is a type of wood)
'worker starts to chop hard' is the wordplay.
'worker' becomes 'bee' (a worker bee).
'starts to' suggests taking the first letters.
The first letters of 'chop hard' is 'ch'.
'bee'+'ch'='BEECH'
(Other definitions for beech that I've seen before include "Common forest tree" , "Common deciduous tree" , "Tree variety" , "Deciduous tree with smooth grey bark" , "Nut-bearing tree" .)