Cavalier is solitary, abandoned (8)
I believe the answer is:
royalist
'cavalier' is the definition.
(Cavaliers were royalists in the English Civil War)
'solitary abandoned' is the wordplay.
'abandoned' indicates an anagram.
'solitary' with letters rearranged gives 'ROYALIST'.
'is' acts as a link.
(Other definitions for royalist that I've seen before include "rightwinger?" , "Supporter of monarchy" , "12 (anag)" , "Monarchist" , "Solitary kind of person who favours monarchy" .)