Single sort of royalist (8)
I believe the answer is:
solitary
'single' is the definition.
(synonyms)
'sort of royalist' is the wordplay.
'sort of' indicates an anagram.
'royalist' with letters rearranged gives 'SOLITARY'.
(Other definitions for solitary that I've seen before include "Left alone" , "On one's own" , "unique" , "Secluded, isolated" , "Existing alone" .)