Authentic maiden in kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(kingdom is a type of country or realm)
'authentic maiden' is the wordplay.
'authentic' becomes 'real' (I've seen this before).
'maiden' becomes 'm' (cricket abbreviation).
'real'+'m'='REALM'
'in' acts as a link.
(Other definitions for realm that I've seen before include "Peers are possessed by this" , "Kingdom, or field of activity" , "A Nation" , "the UK, perhaps" , "Area of interest/activity" .)