Clergyman is to lose his head soon (4)

I believe the answer is:

anon

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'soon' is the definition.
(synonyms)

I cannot understand how the remainder of the clue works.

(Other definitions for anon that I've seen before include "Soon; unattributed" , "Soon - unknown author (abbr)" , "Having no known name" , "Soon, precious stone" , "Not identified by name" .)

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