Decapitated poet’s killers (5)

I believe the answer is:

orcas

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'killers' is the definition.
('orca' can be a synonym of 'killer')

I don't understand how the remainder of the clue works.

(Other definitions for orcas that I've seen before include "Killers" , "Killer whales" .)

I've seen this clue in The Times.

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