The most common and most likely answer to this crossword clue is the 6 letter word BEWAIL
I've seen this crossword clue in The Times
B
E
W
A
I
L
More clues leading to the result BEWAIL
Buddy explains!

The straight part
We know that "Moan about" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moan about = bewail.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 BEWAIL mean?
BEWAIL verb- To wail over; to feel or express deep sorrow for