Oppose nobleman and queen (7)
I believe the answer is:
counter
'oppose' is the definition.
(I've seen this before)
'nobleman and queen' is the wordplay.
'nobleman' becomes 'count' (count is a type of aristocrat).
'and' means one lot of letters go next to another.
'queen' becomes 'ER' (short for Elizabeth Regina ie Queen Elizabeth).
'count'+'er'='COUNTER'
(Other definitions for counter that I've seen before include "Parry" , "It's quite the opposite" , "part of stern" , "Small game disc; oppose" , "Game piece; oppose" .)