The most common and most likely answer to this crossword clue is the 8 letter word DECADENT
I've seen this crossword clue in The Times
D
E
C
A
D
E
N
T
More clues leading to the result DECADENT
- Declining November temperature going beyond 40s?
- Very bad plug with nice wrapping
- Morally corrupt equivalent of ten depressions?
- After ten years, books degraded
- Immoral collection of books appearing after a number of years
- Ten years associated with heartless nest, corrupt
- A negative effect at the end of last month’s declining
- Effete English rogue gripped by depression
- Perhaps Blair years ultimately written about as corrupt
- Books on period being immoral
Buddy explains!

The straight part
We know that "Morally corrupt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case morally corrupt = decadent.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 DECADENT mean?
DECADENT noun- A person affected by moral decay.
- Characterized by moral or cultural decline.
- Luxuriously self-indulgent.