The most common and most likely answer to this crossword clue is the 11 letter word DOWNHEARTED
I've seen this crossword clue in The Daily Telegraph
D
O
W
N
H
E
A
R
T
E
D
More clues leading to the result DOWNHEARTED
Buddy explains!

The straight part
We know that "dejected" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dejected = downhearted.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 DOWNHEARTED mean?
DOWNHEARTED adjective- Sad, discouraged, in low spirits, unhappy, having no hope