Kingdom certainly not without king (6)
I believe the answer is:
norway
'kingdom' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'certainly not without king' is the wordplay.
'certainly not' becomes 'no way' (both are emphatically negative answers).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'king' becomes 'R' (abbreviation for rex, king in Latin).
'noway' enclosing 'r' is 'NORWAY'.
Can you help me to learn more?
(Other definitions for norway that I've seen before include "Mountainous country" , "Northern European country" , "European monarchy" , "North European country" , "in E" .)