The most common and most likely answer to this crossword clue is the 9 letter word LOOSELEAF
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More clues leading to the result LOOSELEAF
Buddy explains!

The straight part
We know that "unbound" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unbound = looseleaf.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 LOOSELEAF mean?
LOOSELEAF noun- (mass noun) Lined paper, usually collected in a binder.
- Consisting of loose leaves (pages), often collected in a binder, rather than being bound like a book or stapled.