Superficial couple upset maiden's lion (3,11)
I believe the answer is:
two dimensional
'superficial' is the definition.
(thesaurus)
'couple upset maiden's lion' is the wordplay.
'couple' becomes 'two' (two people or things).
'upset' indicates anagramming the letters.
'maidens'+'lion'='maidenslion'
'maidenslion' with letters rearranged gives 'dimensional'.
'two'+'dimensional'='TWO-DIMENSIONAL'
(Other definitions for two dimensional that I've seen before include "Like a plane" , "Lacking depth" , "Flat" .)