Poet is excluded, by the sound of it (4)
I believe the answer is:
bard
'poet' is the definition.
(I know that bard is a type of poet)
'excluded by the sound of it' is the wordplay.
'excluded' becomes 'barred' ('bar' can be a synonym of 'exclude').
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'barred' is a homophone of 'BARD'.
'is' is the link.
(Other definitions for bard that I've seen before include "Gray, perhaps" , "Traditional poet" , "Celtic poet" , "Ancient poet" , "Poet; sounds like forbidden" .)