Describe former lover? Unattractive (7)
I believe the answer is:
explain
'describe' is the definition.
(I've seen this before)
'former lover? unattractive' is the wordplay.
'former lover?' becomes 'ex'.
'unattractive' becomes 'plain' ('plain' can be similar in meaning to 'unattractive').
'ex'+'plain'='EXPLAIN'
(Other definitions for explain that I've seen before include "Elucidate, clarify" , "Justify" , "Describe" , "Elucidate - define" , "offer clarification" .)