The most common and most likely answer to this crossword clue is the 9 letter word DESCARTES
I've seen this crossword clue in The Guardian
D
E
S
C
A
R
T
E
S
More clues leading to the result DESCARTES
- Partially downgrades car tested by mathematician
- French philosopher who thought SS created mayhem
- Group hurried up, catching second 8
- French philosopher’s awfully sad secret
- French thinker
- Sad secret disturbed philosopher
- Philosopher extremely disagreeable actress upset
- Philosopher, self-proclaimed existential thinker?
- Philosopher grades car tested in part
- Pioneer using coordinates in some maps from France
Buddy explains!
The straight part
We know that "French philosopher who thought" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case french philosopher who thought = descartes.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.