Civil War royalist (8)
I believe the answer is:
cavalier
'civil war royalist' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cavalier that I've seen before include "Showing a lack of proper concern" , "'Thoughtless, offhand (8)'" , "A vile car is offhand" , "... King Charles, canine breed" , "Offhand - gentleman escorting lady" .)