Sing to a new person (5)
I believe the answer is:
human
'person' is the definition.
(I know that person can be written as Human)
'sing to a new' is the wordplay.
'sing' becomes 'hum' (humming is a kind of singing).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'hum'+'a'+'n'='HUMAN'
(Other definitions for human that I've seen before include "Mortal; compassionate" , "Like a real person" , "Relating to mankind" , "likely to err?" , "Like people" .)