The most common and most likely answer to this crossword clue is the 7 letter word PASTEUR
I've seen this crossword clue in Financial Times
P
A
S
T
E
U
R
More clues leading to the result PASTEUR
- Old Frenchman's grazing cattle finally moving forward
- Some cruets apparently brought back for chemist
- Chemist has sticker across uniform
- Doctor captures headless French scientist
- Bacteriologist's gone his own way in retirement
- Man of science tears up novel
- Fix case of ulcer, as chemist
- Stick with original scientist
- Famous chemist over half the continent
- French chemist detailed former currency?
Buddy explains!

The straight part
We know that "Famous chemist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case famous chemist = pasteur.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.