Not at all like a married couple (5)
I believe the answer is:
unwed
'not at all like a married couple' is the definition.
I can't judge whether this defines the answer.
'not at all like' is the wordplay.
'not' becomes 'un' (I've seen this in other clues).
'at' means one lot of letters go next to another.
'all like' becomes 'wed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'un'+'wed'='UNWED'
Can you help me to learn more?
(Other definitions for unwed that I've seen before include "Not married" , "Divorced" , "Single" , "Without benefit of clergy?" .)