Unproductive peer mentioned in speech (6)
I believe the answer is:
barren
'unproductive' is the definition.
('barren' can be a synonym of 'unproductive')
'peer mentioned in speech' is the wordplay.
'peer' becomes 'baron' (baron is a kind of peer).
'mentioned in speech' indicates a 'sounds like' (homophone) clue.
'baron' sounds like 'BARREN'.
(Other definitions for barren that I've seen before include "Bare and bleak" , "Unproductive; bleak" , "By way of illustration" , "Producing little vegetation" , "Unproductive, arid" .)