The most common and most likely answer to this crossword clue is the 8 letter word LUKEWARM
I've seen this crossword clue in The Daily Telegraph
L
U
K
E
W
A
R
M
More clues leading to the result LUKEWARM
- Cool evangelist, friendly
- Half-hearted saint with inadequate bunch of fighters
- Not enthused by abstract mural surrounding gardens
- Apathetic Liberal member touring posh gardens
- Mark’s successor fighting Mark with little ardour
- Conflict between evangelist and medium lacking conviction
- Evangelist with detachment is half-hearted
- Half-hearted conflict found in gospel
- Evangelist fighting against atheism ultimately becomes half-hearted
- Half-hearted, hot gospeller originally
Buddy explains!

The straight part
We know that "Half-hearted" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case half-hearted = lukewarm.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 LUKEWARM mean?
LUKEWARM adjective- (temperature) Between warm and cool.
- Not very enthusiastic (about a proposal or an idea).