A great deal may be killed (4)
I believe the answer is:
slew
I believe this is a double definition.
'a great deal' is the first definition.
('slew' can be a synonym of 'great deal')
'be killed' is the second definition.
(historical past tense of slay)
'may' acts as a link.
(Other definitions for slew that I've seen before include "Large number -- killed" , "Dispatched" , "Turn uncontrollably" , "Twist sideways" , "Killed long ago" .)