Married couple seizes opportunity to do something (4)
I believe the answer is:
time
'something' is the definition.
(I know that time is a something)
'married couple seizes' is the wordplay.
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'couple' becomes 'tie' (both can mean to join).
'seizes' means one lot of letters goes inside another.
'm' going into 'tie' is 'TIME'.
'opportunity to do' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for time that I've seen before include "Pub closing call" , "See 12" , "Bird" , "Prison sentence; tempo" , "Procrastination is the thief of ." .)