A large number killed (4)
I believe the answer is:
I believe this is a double definition.
'a large number' is the first definition.
(slew can mean a large amount of something)
'killed' is the second definition.
(historical past tense of slay)
(Other definitions for slew that I've seen before include "Killed - swing" , "Change direction abruptly" , "Slaughtered" , "Uncontrollable turn/slide" , "Large number -- killed" .)