The most common and most likely answer to this crossword clue is the 9 letter word CONFIDANT
I've seen this crossword clue in The Daily Telegraph
C
O
N
F
I
D
A
N
T
Buddy explains!

The straight part
We know that "Close friend" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case close friend = confidant.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 CONFIDANT mean?
CONFIDANT noun- A person in whom one can confide or share one's secrets: a friend.