Sailor finds the French skilful (4)
I believe the answer is:
able
'skilful' is the definition.
(I've seen this before)
'sailor finds the french' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'finds' 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" , "accomplished" , "Skilled" , "Capable seaman" , "Competent as, say, sailor" .)