Start chess, ultimately, with pawn (5)
I believe the answer is:
shock
'start' is the definition.
(thesaurus)
'chess ultimately with pawn' is the wordplay.
'ultimately' indicates one should take the final letters.
'with' is a charade indicator (letters next to each other).
'pawn' becomes 'hock' (hock can mean to pawn an item at a pawnbroker's).
The last letter of 'chess' is 's'.
's'+'hock'='SHOCK'
(Other definitions for shock that I've seen before include "Unpleasant surprise" , "Appal" , "Stun" , "Horrify - stroke" , "old dog is > sixty!" .)