One-time pro associated with French sea (6)
I believe the answer is:
former
'one-time' is the definition.
(I've seen this in another clue)
'pro associated with french sea' is the wordplay.
'pro' becomes 'for' (I've seen this before).
'associated with' says to put letters next to each other.
'french sea' becomes 'mer' ('sea' in French).
'for'+'mer'='FORMER'
(Other definitions for former that I've seen before include "Past; first (of two)" , "One shaping" , "First-mentioned" , "The first of two, earlier" , "Core for winding an electrical core" .)