The most common and most likely answer to this crossword clue is the 11 plus 7 letter word Unspecified ordinal
I've seen this crossword clue in The Guardian
U
n
s
p
e
c
i
f
i
e
d
o
r
d
i
n
a
l
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.