Revolutionary worker in application for singer (9)
I believe the answer is:
chanteuse
'singer' is the definition.
(I've seen this before)
'revolutionary worker in application' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'worker' becomes 'ant' (worker is a type of ant).
'in' is an insertion indicator.
'application' becomes 'use' (I've seen this in another clue).
'che' going around 'ant' is 'chante'.
'chante'+'use'='CHANTEUSE'
'for' is the link.
(Other definitions for chanteuse that I've seen before include "French female singer in tune chase" , "Female popular singer" , "A French woman singer of popular ballads" , "Female singer, in a nightclub perhaps" , "Female cabaret singer" .)