The most common and most likely answer to this crossword clue is the 12 letter word INCONSOLABLE
I've seen this crossword clue in The Times
I
N
C
O
N
S
O
L
A
B
L
E
Buddy explains!
The straight part
We know that "Moaning endlessly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case moaning endlessly = inconsolable.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 INCONSOLABLE mean?
INCONSOLABLE adjective- Not consolable; unable to be consoled or comforted, usually due to grief, disappointment, or other distress.