State of equality a capital city is missing (3)
I believe the answer is:
par
'state of equality' is the definition.
(I've seen this before)
'a capital city is missing' is the wordplay.
'a capital city' becomes 'paris' (capital of France).
'missing' suggests deleting specific letters.
'paris' with 'is' taken out is 'PAR'.
(Other definitions for par that I've seen before include "Target score (golf)" , "Face value; equal standing" , "Usual score at golf" , "Rap for being average" , "Black music" .)