Authority of the monarch faced by wartime detainee (5)
I believe the answer is:
power
'authority' is the definition.
(I've seen this before)
'the monarch faced by wartime detainee' is the wordplay.
'the monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen).
'faced by' says to put letters next to each other.
'wartime detainee' becomes 'pow' (I am not sure about this - if you are sure you should believe this answer much more).
'er' put after 'pow' is 'POWER'.
'of' is the link.
Can you help me to learn more?
(Other definitions for power that I've seen before include "Electricity or strength" , "Military potential" , "Control and influence exercised over others" , "military force" , "Possession of controlling influence" .)