Antecedent, harbinger (10)
I believe the answer is:
forerunner
I believe this clue is a double definition.
'antecedent' is the first definition.
(I know that antecedent can be written as forerunner)
'harbinger' is the second definition.
(I know that harbinger can be written as forerunner)
(Other definitions for forerunner that I've seen before include "one coming ahead" , "Precursor" .)