This type of clue is back — without a couple of letters, it's a killer! (4)
I believe the answer is:
orca
'it's a killer' is the definition.
(orca is a term for the killer whale)
I cannot understand how the rest of the clue works.
(Other definitions for orca that I've seen before include "27 [WHALE]" , "ship" , "School killer" , "Large mammal" , "swimmer in black and white" .)