The most common and most likely answer to this crossword clue is the 9 letter word EXPATIATE
I've seen this crossword clue in Financial Times
E
X
P
A
T
I
A
T
E
More clues leading to the result EXPATIATE
- Give details of displaced person one took in
- Elaborate purge repressing returning former reservists
- . Elaborate exile having run away
- With king banished, émigré at length set forth
- Go into detail about former head embracing return of old reading aid
- Elaborate riff’s intro left out of An American in Paris indefinitely?
- Person overseas, seeing abdication of Queen, is to say more
- Discourse from displaced person right away
- Speak at length with person living overseas missing queen
Buddy explains!

The straight part
We know that "Go into detail" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case go into detail = expatiate.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 EXPATIATE mean?
EXPATIATE verb- To range at large, or without restraint.
- To write or speak at length; to be copious in argument or discussion.
- To expand; to spread; to extend; to diffuse; to broaden.