The most common and most likely answer to this crossword clue is the 8 letter word EXCURSUS
I've seen this crossword clue in The Times
E
X
C
U
R
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U
S
More clues leading to the result EXCURSUS
Buddy explains!
The straight part
We know that "discussion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case discussion = excursus.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 EXCURSUS mean?
EXCURSUS noun- A fuller treatment (in a separate section) of a particular part of the text of a book, especially a classic.
- A narrative digression, especially to discuss a particular issue.