Saying from the commercial era (5)
I believe the answer is:
adage
'saying' is the definition.
(adage is a kind of saying)
'the commercial era' is the wordplay.
'the commercial' becomes 'ad' (abbreviation for advertisement).
'era' becomes 'age' (both can mean a long period of time).
'ad'+'age'='ADAGE'
'from' acts as a link.
(Other definitions for adage that I've seen before include "Old saying, maxim" , "Saying, saw" , "Short statement expressing a general truth" , "Well-remembered proverb or saying" , "Axiom" .)