Jolly piratical bonehead? (5)

I believe the answer is:

skull

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'jolly piratical bonehead?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

This is all the clue.

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(Other definitions for skull that I've seen before include "Bony part of head" , "Enclosure for the brain" , "Cranium" , "Head structure" , "Bony case of brain" .)

I've seen this clue in the Evening Standard.

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