Assist excellent daughter (3)
I believe the answer is:
aid
'assist' is the definition.
(synonyms)
'excellent daughter' is the wordplay.
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'daughter' becomes 'd' (genealogical abbreviation).
'ai'+'d'='AID'
(Other definitions for aid that I've seen before include "A hand" , "charity" , "welfare" , "Care, assistance" , "Auxiliary" .)