He was famous as a chemist over half Europe (7)
I believe the answer is:
pasteur
'he was famous as a chemist' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'over half europe' is the wordplay.
'over' becomes 'past' (I've seen this in another clue).
'half' suggests halving the letters.
'europe' with half the letters taken is 'eur'.
'past'+'eur'='PASTEUR'
Can you help me to learn more?
(Other definitions for pasteur that I've seen before include "Louis --, French bacteriologist" , "French chemist and biologist (1822-1895)" , "Louis -, nineteenth century French chemist" , "French scientist" , "French chemist and biologist, d. 1895" .)