Single man, ruder possibly, maintaining ego (9)
I believe the answer is:
unmarried
'single' is the definition.
(I've seen this before)
'man ruder possibly maintaining ego' is the wordplay.
'possibly' indicates anagramming the letters.
'maintaining' is an insertion indicator.
'ego' becomes 'i'.
'man'+'ruder'='manruder'
'manruder' is an anagram of 'unmarred'.
'unmarred' enclosing 'i' is 'UNMARRIED'.
(Other definitions for unmarried that I've seen before include "Not yet wed" , "Status of a bachelor" , "Single in terms of partnership" .)