Hurt, only missing line for balance (7)
I believe the answer is:
harmony
'balance' is the definition.
(thesaurus)
'hurt only missing line' is the wordplay.
'hurt' becomes 'harm' ('harm' can be a synonym of 'hurt'**).
'missing' suggests deleting specific letters.
'line' becomes 'l'.
'only' with 'l' taken out is 'ony'.
'harm'+'ony'='HARMONY'
'for' is the link.
(Other definitions for harmony that I've seen before include "Agreement, concord" , "Pleasing combination of musical notes" , "Accord" , "Sweet or melodious sound, no disagreement" , "Mutual rapport" .)