The most common and most likely answer to this crossword clue is the 7 letter word UNHAPPY
I've seen this crossword clue in The Guardian
U
N
H
A
P
P
Y
Buddy explains!

The straight part
We know that "miserable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case miserable = unhappy.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 UNHAPPY mean?
UNHAPPY noun- An individual who is not happy.
- Not happy; sad.
- Not satisfied; unsatisfied.
- Not lucky; unlucky.
- Not suitable; unsuitable.