Eager to behead the king of Israel (4)
I believe the answer is:
avid
'eager' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for avid that I've seen before include "Excessively keen" , "Extremely keen" , "Greedy or eagerly desirous" , "Very keen, desirous" , "Keenly interested" .)