The most common and most likely answer to this crossword clue is the 4 plus 5 letter word TELL APART
T
E
L
L
A
P
A
R
T
More clues leading to the result TELL APART
- Distinguish between two types of split
- Distinguish between lines embraced by far right group — almost
- Distinguish between section following order to advance
- Pick out unfinished carrying surface, the kind fork-lifts take back
- Spot the difference — William’s on a roll, they say
- Perhaps William’s on a roll as they say, can you differentiate?
- Differentiate between, say, William and Arthur sharing a penny?
Buddy explains!

The straight part
We know that "Spot the difference" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spot the difference = tell apart.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.