Western worker's deficiency (4)
I believe the answer is:
want
'deficiency' is the definition.
('want' can be a synonym of 'deficiency')
'western worker's' is the wordplay.
'western' becomes 'w'.
'worker' becomes 'ant' (worker is a type of ant).
'w'+'ant'='WANT'
(Other definitions for want that I've seen before include "Wish" , "Need or desire" , "Desire to possess" , "'Wilful waste makes woeful . . . .'" , "Desire - deficiency" .)