Dismisses (5)
(Other definitions for sacks that I've seen before include "Bags; wines" , "rifles" , "Plunders; bags" , "Fires; large bags" , "Large strong bags" .)
'dismisses' is the definition.
('fire' can be a synonym of 'dismiss')
This is the entire clue.
(Other definitions for fires that I've seen before include "Cashiers" , "Sacks; conflagrations" .)