The most common and most likely answer to this crossword clue is the 10 letter word OSCULATORY
I've seen this crossword clue in The Guardian
O
S
C
U
L
A
T
O
R
Y
Buddy explains!
The straight part
We know that "Sort of advance one may meet under 10" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sort of advance one may meet under 10 = osculatory.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.