The most common and most likely answer to this crossword clue is the 9 letter word SUBSCRIPT
I've seen this crossword clue in The Times
S
U
B
S
C
R
I
P
T
More clues leading to the result SUBSCRIPT
Buddy explains!

The straight part
We know that "Small number possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case small number possibly = subscript.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 SUBSCRIPT mean?
SUBSCRIPT noun- A type of lettering form written lower than the things around it.
- A numerical index into an array.
- (of a variable) To provide with a subscript.
- (of a text) To convert to a subscript form.
- Written underneath.