The most common and most likely answer to this crossword clue is the 8 letter word TRYSTING
I've seen this crossword clue in The Guardian
T
R
Y
S
T
I
N
G
Buddy explains!

The straight part
We know that "meeting in secret" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case meeting in secret = trysting.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 TRYSTING mean?
TRYSTING verb- To make a tryst; to agree to meet at a place.
- To arrange or appoint (a meeting time etc.).
- To keep a tryst, to meet at an agreed place and time.
- An appointment; a tryst.