The most common and most likely answer to this crossword clue is the 4 letter word MOPE
I've seen this crossword clue in The Times
M
O
P
E
More clues leading to the result MOPE
- Medical man with drill causing misery
- Brood accommodated in Palermo, perhaps
- Horrible poem makes one look gloomy
- Medical man with drill — result, misery
- Drop head in second exercise
- Maureen facing gym gets to be depressed
- Pine from lightweight transport with end removed
- Look down on people initially invading Middle East
- Feel dejected after daughter falls off scooter
- Complain when doctor introduces exercise
Buddy explains!

The straight part
We know that "Brood" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case brood = mope.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 MOPE mean?
MOPE noun- A dull, spiritless person.
- (pornography industry) A bottom feeder who "mopes" around a pornography studio hoping for his big break and often does bit parts in exchange for room and board and meager pay.
- To carry oneself in a depressed, lackadaisical manner; to give oneself up to low spirits; to pout, sulk.
- To make spiritless and stupid.