Model -- and not married (4)
I believe the answer is:
norm
'model' is the definition.
(I've seen this in another clue)
'and not married' is the wordplay.
'and not' becomes 'nor' ('nor' means 'and also not').
'married' becomes 'm'.
'nor'+'m'='NORM'
(Other definitions for norm that I've seen before include "Standard considered to be representative" , "Standard choice" , "Required or acceptable standard" , "expected thing" , "Average level of performance" .)