Competent-sounding son of leading man (4)
I believe the answer is:
able
'competent' is the definition.
(similar in meaning)
'sounding son of leading man' is the wordplay.
'sounding' indicates a 'sounds like' (homophone) clue.
'son of leading man' becomes 'abel' (son of Adam, the first man in the Bible).
'abel' sounds like 'ABLE'.
(Other definitions for able that I've seen before include "Clever skilful" , "- -bodied; - seaman" , "showing talent" , "displaying skill" , "Bale out, being competent" .)