Eager to behead the king of Israel (4)

I believe the answer is:

avid

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'eager' is the definition.
(synonyms)

I can't explain the remainder of the clue.

(Other definitions for avid that I've seen before include "Excessively keen" , "Extremely keen" , "Greedy or eagerly desirous" , "Very keen, desirous" , "Keenly interested" .)

I've seen this clue in The Globe and Mail, The Telegraph and The Guardian.

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