Saw a daughter getting mature (5)
I believe the answer is:
adage
'saw' is the definition.
(saw can mean a proverb or saying)
'a daughter getting mature' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'getting' means one lot of letters go next to another.
'mature' becomes 'age' (synonyms).
'a'+'d'+'age'='ADAGE'
(Other definitions for adage that I've seen before include "say it again and again!" , "Axiom" , "True proverb or saying" , "Old saw" , "Old saying; proverb" .)