Once ran from French convert (6)
I believe the answer is:
'convert' is the definition.
(I know that encode is a type of convert)
'once ran from french' is the wordplay.
'ran' indicates an anagram (letters have run around).
'from french' becomes 'de' (French for 'from').
'once' anagrammed gives 'enco'.
(Other definitions for encode that I've seen before include "Put (message) into ciphers" , "Convert into a cipher" , "transform with substitutions?" , "Put into secret writing" , "Encipher" .)