The most common and most likely answer to this crossword clue is the 9 letter word GERUNDIVE
I've seen this crossword clue in The Guardian
G
E
R
U
N
D
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V
E
More clues leading to the result GERUNDIVE
Buddy explains!

The straight part
We know that "Verbal adjective" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case verbal adjective = gerundive.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 GERUNDIVE mean?
GERUNDIVE noun- (in Latin grammar) a verbal adjective that describes obligation or necessity, equivalent in form to the future passive participle.
- (less commonly, in English grammar) a verbal adjective ending in -ing , also called a "present participle".
- Gerundial