National workers' group taking on half of work (4)
I believe the answer is:
turk
'national' is the definition.
(I know that Turk is a type of national)
'workers' group taking on half of work' is the wordplay.
'workers' group' becomes 'tu' (short for trade union).
'taking on' means one lot of letters go next to another.
'half of' indicates taking half.
'work' halved is 'rk'.
'tu'+'rk'='TURK'
(Other definitions for turk that I've seen before include "Native of Izmir or Ankara" , "impetuous as a youth" , "West Asian" , "Native of Ankara's country" , "Resident of Ankara maybe" .)