The most common and most likely answer to this crossword clue is the 10 letter word UNNUMBERED
I've seen this crossword clue in The Daily Telegraph
U
N
N
U
M
B
E
R
E
D
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 UNNUMBERED mean?
UNNUMBERED adjective- Not identified with a number
- Too numerous to be counted; countless or innumerable