Old-fashioned relative moves forward (6,2)
I believe the answer is:
passes on
'moves forward' is the definition.
'old-fashioned relative' is the wordplay.
'old-fashioned' becomes 'passe' (synonyms).
'relative' becomes 'son' (son is a kind of relative).
'passe'+'son'='PASSES ON'
(Other definitions for passes on that I've seen before include "Dies; transmits" , "graduates" , "Hands to the next person" .)