Competent seaman with the French (4)
I believe the answer is:
able
'competent' is the definition.
(similar in meaning)
'seaman with the french' is the wordplay.
'seaman' becomes 'ab' (short for able seaman).
'with' is a charade indicator (letters next to each other).
'the french' becomes 'le' ('the' in French).
'ab'+'le'='ABLE'
(Other definitions for able that I've seen before include "See 10" , "Qualified - expert" , "Having great proficiency or intelligence" , "displaying skill" , "Competent as seaman may be" .)