Peripheral dictionary includes 'indicative of something to come' (8)
I believe the answer is:
heraldic
'indicative of something to come' is the definition.
(relating to heralds or things which herald)
'peripheral dictionary includes' is the wordplay.
'includes' indicates the answer is hidden within the clue.
'HERALDIC' is hidden in the letters of 'peripheral dictionary'.
(Other definitions for heraldic that I've seen before include "Of armorial bearings" , "Of family crests" , "of the coat of arms" , "show of arms" , "Relating to officers who register genealogies" .)