Notice French king, with time, becomes skilful (6)
I believe the answer is:
adroit
'skilful' is the definition.
(adroit can mean skilful or masterful)
'notice french king with time' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'french king' becomes 'roi' ('king' in French).
'with' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'ad'+'roi'+'t'='ADROIT'
'becomes' acts as a link.
(Other definitions for adroit that I've seen before include "resourceful" , "Quick or skilful" , "Skilful, dexterous" , "Quick and clever in action or thought" , "Dexterous, artful" .)