The most common and most likely answer to this crossword clue is the 8 plus 5 letter word STEPPING STONE
I've seen this crossword clue in The Daily Telegraph
S
T
E
P
P
I
N
G
S
T
O
N
E
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 STEPPING STONE mean?
STEPPING STONE noun- A stone that can be stepped on in crossing something, especially a marsh or creek.
- Something used as a way to progress to something or somewhere else.