The most common and most likely answer to this crossword clue is the 3 letter word PHI
P
H
I
More clues leading to the result PHI
- Letter recently ignored in stamp collecting
- Letter from the Balkans, far from neutral
- Character needed to get the measure of acid test?
- Letter of public house, opening for inspection
- Character recently abandoning collector’s hobby
- Homer's initial appears in irrational letter to Greeks
- Hard dividing an irrational number, which Diophantus once showed
- Horse caught by one Greek character or another
- Greek character’s fractured hip
- Quietly greeting letter from Greece
Buddy explains!

The straight part
We know that "Greek character" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case greek character = phi.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 PHI mean?
PHI noun- Φ, the 21st letter of the Euclidean and modern Greek alphabet, usually romanized as "ph".
- The golden ratio.
- A visual illusion whereby a sequential pattern of lights produces a false sense of motion.