Nobleman - unproductive, so we hear (5)
I believe the answer is:
baron
'nobleman' is the definition.
(baron is a kind of nobleman)
'unproductive so we hear' is the wordplay.
'unproductive' becomes 'barren' (synonyms).
'so we hear' shows a homophone (sound like).
'barren' is a homophone of 'BARON'.
(Other definitions for baron that I've seen before include "British peer of the lowest rank" , "Title of rank" , "Nobleman providing a portion of beef" , "powerful man owning lots of dailies?" , "Lowest rank of British peerage" .)