A turn before (3)
I believe the answer is:
ago
'before' is the definition.
(eg years ago means year before)
'a turn' is the wordplay.
'turn' becomes 'go' (a person's move in a board game).
'a'+'go'='AGO'
(Other definitions for ago that I've seen before include "In past times" , "Earlier, gone by" , "Gone, past, since" , "Time past" , "(Years) before the present time" .)