The most common and most likely answer to this crossword clue is the 10 letter word EVANGELIST
I've seen this crossword clue in Independent
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More clues leading to the result EVANGELIST
- Spinning line, TV sage is one preaching
- Film about Greek musician and creator of gospel
- Preacher performing live on stage lacks authority essentially
- Welshman wrapping one leg around head of travelling preacher
- Zealous believer of Everlasting King taken out and shot
- One adopting the missionary position?
- Missionary agents live abroad
- Perhaps leaving set with missionary?
- Preacher sent via potentially captivating setter?
- A live gent’s becoming excited as a preacher
Buddy explains!

The straight part
We know that "Zealous believer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case zealous believer = evangelist.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EVANGELIST mean?
EVANGELIST noun- An itinerant or special preacher, especially a revivalist, who conducts services in different cities or locations, now often televised.
- A writer of a gospel, especially the four New Testament Gospels (Matthew, Mark, Luke, and John), usually Evangelist.
- (primitive Church) A person who first brought the gospel to a city or region.
- (Mormon Church) A patriarch.
- A person marked by extreme enthusiasm for or support of any cause, particularly with regard to religion.
- A person hired to promote a particular technology.