True maiden in kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(kingdom is a type of country or realm)
'true maiden' is the wordplay.
'true' becomes 'real' (similar in meaning).
'maiden' becomes 'm' (cricket abbreviation).
'real'+'m'='REALM'
'in' acts as a link.
(Other definitions for realm that I've seen before include "Monarchy" , "Land under a king or queen" , "field of study" , "Knowledge base" , "Empire - state" .)