The most common and most likely answer to this crossword clue is the 9 letter word UNPLANNED
I've seen this crossword clue in The Guardian
U
N
P
L
A
N
N
E
D
Buddy explains!

The straight part
We know that "not intended" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not intended = unplanned.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 UNPLANNED mean?
UNPLANNED adjective- Unintentional; not intended
- Spontaneous and not thought through in advance
- Not having any structure or organization