Promise man bread with this starter (8)
I believe the answer is:
covenant
'promise' is the definition.
(I've seen this before)
'man bread with this starter' is the wordplay.
'man' becomes 'cove' (I've seen this in other clues**).
'bread' becomes 'nan' (variant spelling of naan).
'with' means one lot of letters go next to another.
'starter' says to take the initial letters.
The initial letter of 'this' is 't'.
'cove'+'nan'+'t'='COVENANT'
(Other definitions for covenant that I've seen before include "Formal agreement of contract" , "Concordat, compact" , "Solemn agreement" , "Formal binding agreement" , "Contract made in a convent" .)