Past events (7)
(Other definitions for bygones that I've seen before include "Let these be these to forgive and forget" , "Things belonging to the past" , "Let ....... be .......; don't hold grudge" , "past events" , "Let - be - means to forget past differences" .)
'past events' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for history that I've seen before include "Time passed" , "Study of past events" , "The record of past events" , "'... repeats itself'" , "Chronicle" .)