Agreed about spiteful woman being involved (11)
I believe the answer is:
complicated
'being involved' is the definition.
(thesaurus)
'agreed about spiteful woman' is the wordplay.
'agreed' becomes 'complied' (complying is a kind of agreeing**).
'about' means one lot of letters goes inside another.
'spiteful woman' becomes 'cat'.
'complied' enclosing 'cat' is 'COMPLICATED'.
(Other definitions for complicated that I've seen before include "consisting of many interconnecting parts" , "Tricky" , "Intricate, difficult" , "confused" , "Not simple" .)