Famous musician stuns sailor (4,4)
I believe the answer is:
rock star
'famous musician' is the definition.
(I've seen this before)
'stuns sailor' is the wordplay.
'stuns' becomes 'rocks'.
'sailor' becomes 'tar' (slang term for a sailor).
'rocks'+'tar'='ROCK STAR'
(Other definitions for rock star that I've seen before include "Bono, say" , "Pop idol" , "David Bowie or Prince, say" , "Musician with groupies?" , "Very famous pop singer" .)