The most common and most likely answer to this crossword clue is the 7 letter word PENT-UP
I've seen this crossword clue in Financial Times
P
E
N
T
-
U
P
More clues leading to the result PENT-UP
Buddy explains!
The straight part
We know that "unable to be released" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unable to be released = pent-up.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 PENT-UP mean?
PENT-UP adjective- Not expressed
- Repressed or suppressed, especially of emotions or impulses