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 tell whether this defines the answer.
'not at all like a married' is the wordplay.
I cannot quite see how this works, but
'not' could be 'un' (prefix meaning 'not') and 'un' is found within the answer.
'married' could be 'wed' (wed can mean married) and 'wed' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
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?" .)