One writes to the French thunder god (6)
I believe the answer is:
author
'one writes' is the definition.
(I've seen this before)
'to the french thunder god' is the wordplay.
'to the french' becomes 'au' ('to the' in French).
'thunder god' becomes 'thor' (I've seen this in another clue).
'au'+'thor'='AUTHOR'
(Other definitions for author that I've seen before include "Ours wrote as Edward" , "Dramatist" , "Someone who originates, causes or initiates something" , "Creator of written work" , "Generator of written work" .)