The most common and most likely answer to this crossword clue is the 5 letter word SHYER
S
H
Y
E
R
Buddy explains!
The straight part
We know that "One having a fling/not so open" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one having a fling/not so open = shyer.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 SHYER mean?
SHYER adjective- Easily frightened; timid.
- Reserved; disinclined to familiar approach.
- Cautious; wary; suspicious.
- Short, insufficient or less than.
- Embarrassed.
- A horse that shies.