Saw a daughter mature (5)
I believe the answer is:
adage
'saw' is the definition.
(saw can mean a proverb or saying)
'a daughter mature' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'mature' becomes 'age' (synonyms).
'a'+'d'+'age'='ADAGE'
(Other definitions for adage that I've seen before include "Old saw" , "Proverb, maxim" , "Short statement expressing a general truth" , "Slogan" , "say it again and again!" .)