. . . a Cardinal unused to staff (6)
I believe the answer is:
newman
'a cardinal' is the definition.
(19th-century Cardinal John Henry Newman)
'unused to staff' is the wordplay.
'unused' becomes 'new' (similar in meaning).
'to staff' becomes 'man' (as in staffing or manning a particular place).
'new'+'man'='NEWMAN'
(Other definitions for newman that I've seen before include "Old Cardinal" , "John Henry --, beatified English cardinal" , "'John Henry ..., founder of what is now UCD (6)'" , "John Henry ---, C19 cardinal" , "Cardinal - PC husband" .)