Accepting second marriage? Together, we're in this (6)
I believe the answer is:
unison
'together we're in this' is the definition.
The definition suggests a singular noun which matches the answer.
'accepting second marriage?' is the wordplay.
'accepting' indicates putting letters inside (inserted letters are accepted).
'second' becomes 's' (common abbreviation).
'marriage?' becomes 'union' (synonyms).
's' inserted inside 'union' is 'UNISON'.
Can you help me to learn more?
(Other definitions for unison that I've seen before include "Total agreement or concord" , "Voices in complete agreement" , "Public service trade union" , "Simultaneous action" , "Accord" .)