The most common and most likely answer to this crossword clue is the 9 letter word UNIPLANAR
U
N
I
P
L
A
N
A
R
Buddy explains!
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 UNIPLANAR mean?
UNIPLANAR adjective- Having, or lying in, a single plane