The most common and most likely answer to this crossword clue is the 5 letter word UNDUE
I've seen this crossword clue in Financial Times
U
N
D
U
E
More clues leading to the result UNDUE
- Some fun duenna finds excessive
- Excessive burns doused periodically
- Excessive, but not expected yet?
- Extravagant jollity not initially expected
- Fun duet; ‘side splitting’? … a bit much
- University dons dancing nude without good reason
- A French affaire d’honneur failing to reach conclusion is not comme il faut
- One from France superior to two from Italy? Inappropriate
- France 1: Italy 2 — that’s too much!
- Not owing what’s excessive
Buddy explains!

The straight part
We know that "without good reason" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case without good reason = undue.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 UNDUE mean?
UNDUE adjective- Excessive; going beyond that what is natural or sufficient.
- That which ought not to be done; illegal; unjustified.
- (of a payment etc) Not owing or payable.