The most common and most likely answer to this crossword clue is the 4 plus 2 plus 3 plus 6 letter word SIGN OF THE ZODIAC
I've seen this crossword clue in The Sunday Telegraph
S
I
G
N
O
F
T
H
E
Z
O
D
I
A
C
More clues leading to the result SIGN OF THE ZODIAC
- Indicator from old Ford Scorpio maybe
- The French discretely invested in bullion libraries — any one of four, or 21
- Cleopatra and Napoleon have one in common
- 27 for example
- One of the houses lit up at night
- Ramshackle zoo's gift: echidna with cancer perhaps
- Leo, say, in big-cat shed with fine for British zoo in a state of disrepair
- Leo possibly seeing good chieftains travelling around end of Suez
Buddy explains!
The straight part
We know that "Cleopatra and Napoleon have one in common" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cleopatra and napoleon have one in common = sign of the zodiac.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.