The most common and most likely answer to this crossword clue is the 5 letter word BUDDY
I've seen this crossword clue in Independent
B
U
D
D
Y
More clues leading to the result BUDDY
Buddy explains!

The straight part
We know that "a friend?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a friend? = buddy.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 BUDDY mean?
BUDDY noun- A friend or casual acquaintance.
- A partner for a particular activity.
- An informal and friendly address to a stranger; a friendly (or occasionally antagonistic) placeholder name for a person one does not know.
- To assign a buddy, or partner, to.
- Resembling a bud.