Clever sailor joining the French (4)
I believe the answer is:
able
'clever' is the definition.
(I've seen this in another clue)
'sailor joining the french' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'joining' says to put 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 "- -bodied; - seaman" , "See 10" , "Bale out, being competent" , "Having the ability to do something" , "Competent as, say, sailor" .)