Most primitive aristocrat that is a good man? (8)
I believe the answer is:
earliest
'most primitive' is the definition.
('early' can be similar in meaning to 'primitive')
'aristocrat that is a good man?' is the wordplay.
'aristocrat' becomes 'earl' (earl is a kind of aristocrat).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'a good man?' becomes 'st' (abbreviation for saint).
'earl'+'ie'+'st'='EARLIEST'
(Other definitions for earliest that I've seen before include "Furthest back in time" , "With the least delay" , "Ateliers (anag.)" , "Nearest the start of a time period" , "Arriving first" .)