Low born donkey (4)
I believe the answer is:
bass
'low' is the definition.
(similar in meaning)
'born donkey' is the wordplay.
'born' becomes 'b' (abbreviation next to the year of someone's birth).
'donkey' becomes 'ass' (ass is a term for a donkey).
'b'+'ass'='BASS'
(Other definitions for bass that I've seen before include "Fish - low voice" , "Very low - perch" , "Lowest register of the male voice" , "Large percussion instrument" , "Freshwater fish and lowest voice" .)