The most common and most likely answer to this crossword clue is the 5 letter word NAIVE
I've seen this crossword clue in The Times
N
A
I
V
E
More clues leading to the result NAIVE
- I will interrupt passage in church, being artless
- Local resident having no time to be green
- Green where spring water comes from, seen travelling west
- One entering part of the church, innocent
- Too trusting, don’t insist on getting name for whiskey
- Green sort of water sent back
- Time to leave local green
- Green paper assimilated by church body
- Innocent one hiding in part of church
- Innocent Methuselah framed by villain on tape
Buddy explains!

The straight part
We know that "Green" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case green = naive.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 NAIVE mean?
NAIVE noun- A naive person; a greenhorn.
- Lacking worldly experience, wisdom, or judgement; unsophisticated.
- Not having been exposed to something.
- (of art) Produced in a simple, childlike style, deliberately rejecting sophisticated techniques.
- Intuitive; designed to follow the way ordinary people approach a problem.