Began; undone (6)
I believe the answer is:
opened
I believe this is a double definition.
'began' is the first definition.
(opening is a kind of beginning)
'undone' is the second definition.
(opening is a kind of undoing)
(Other definitions for opened that I've seen before include "starting the game" , "Began - undone" , "Started, a meeting say" , "Made available" , "Unlocked or unfolded" .)