Actual capital of Minoan domain (5)
I believe the answer is:
realm
'domain' is the definition.
(I know that realm is a type of domain)
'actual capital of minoan' is the wordplay.
'actual' becomes 'real' (similar in meaning).
'capital of' indicates taking the first letters.
The initial letter of 'minoan' is 'm'.
'real'+'m'='REALM'
(Other definitions for realm that I've seen before include "A Nation" , "Kingdom; field of interest" , "department" , "Land under a king or queen" , "field of study" .)