Marriage, matrimony (7)
I believe the answer is:
wedlock
I believe this is a double definition.
'marriage' is the first definition.
(I know that marriage can be written as wedlock)
'matrimony' is the second definition.
(I know that matrimony can be written as wedlock)
(Other definitions for wedlock that I've seen before include "Matrimony" , "Marital state" , "The married state - throw away the key" , "A state of union" , "State of marriage" .)