The most common and most likely answer to this crossword clue is the 9 letter word NIETZSCHE
I've seen this crossword clue in The Daily Telegraph
N
I
E
T
Z
S
C
H
E
More clues leading to the result NIETZSCHE
- Thinker’s uncommon zest during recess
- Final character in set troubled revolutionary philosopher
- Philosopher’s last letter: hence it’s treated specially
- Compound of zinc’s the cure in the end for German intellect
- Creator of Superman, champion wearing size ten pants
- German known to think child should wear size ten pants
- Starts to think zanily, being into crazy Chinese philosopher
- Tense final letter held by confused Chinese philosopher
- Precise sound of cricket on the radio, I thought!
- . Chintzes designed by English philosopher
Buddy explains!

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