Well-known occultist's assistant (8)
I believe the answer is:
familiar
This clue might be a double definition.
'well-known' is the first definition.
(similar in meaning)
'occultist's assistant' is the second definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for familiar that I've seen before include "Well known from long association" , "Well-acquainted with a witch's cat" , "routine" , "Usual; well known" , "Well-known, easily recognised" .)