Married after ring wasn't square (4)
I believe the answer is:
owed
'wasn't square' is the definition.
(I've seen this in another clue)
'married after ring' is the wordplay.
'married' becomes 'wed' (wed can mean married).
'after' means one lot of letters go next to another.
'ring' becomes 'o' (letter resembling a ring).
'wed' put after 'o' is 'OWED'.
(Other definitions for owed that I've seen before include "Had an obligation to pay" , "(Sum) due for payment" , "Was indebted" , "Was due to pay" , "Outstanding" .)