The most common and most likely answer to this crossword clue is the 8 letter word DIOGENES
I've seen this crossword clue in The Times
D
I
O
G
E
N
E
S
More clues leading to the result DIOGENES
- Old Greek perishes after eating melon
- Cynic — one involved in swindle — means to inherit
- Old philosopher stops gathering old information
- Philosopher stops working to get hold of Socrates’ second book
- Cynic died before seeing about having a ball
- Cynic is on edge after conversion
- Philosopher, old and extremely gentle, eats out
- Altered ego is end to philosopher
- Cynic denies God, endlessly exploding
Buddy explains!

The straight part
We know that "Old philosopher" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old philosopher = diogenes.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.