Mean singing voice heard (4)
I believe the answer is:
base
'mean' is the definition.
('base' can be a synonym of 'mean')
'singing voice heard' is the wordplay.
'singing voice' becomes 'bass' (bass is a kind of singing voice).
'heard' indicates a 'sounds like' (homophone) clue.
'bass' sounds like 'BASE'.
(Other definitions for base that I've seen before include "Venial; headquarters" , "Lowest part of something" , "Ignoble, military site" , "This underlying structure" , "Infamous" .)