Low born idiot (4)
I believe the answer is:
bass
'low' is the definition.
('bass' can be similar in meaning to 'low')
'born idiot' is the wordplay.
'born' becomes 'b'.
'idiot' becomes 'ass' (I've seen this before).
'b'+'ass'='BASS'
(Other definitions for bass that I've seen before include "Fish; deep voice" , "Deep-toned" , "Male singer and saltwater fish" , "Sea fish; voice" , "Large percussion instrument" .)