Low born fool (4)
I believe the answer is:
bass
'low' is the definition.
(similar in meaning)
'born fool' is the wordplay.
'born' becomes 'b' (abbreviation next to the year of someone's birth).
'fool' becomes 'ass' (both can mean a stupid person).
'b'+'ass'='BASS'
(Other definitions for bass that I've seen before include "Freshwater fish and lowest voice" , "Male singer and saltwater fish" , "Fish; deep voice" , "Low fellow" , "A fish, or the lowest pitch in music" .)