Mysterious secret inscrutable and occult primarily? (8)
I believe the answer is:
esoteric
'mysterious' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for esoteric that I've seen before include "Aimed at a few" , "Intelligible only to the initiated" , "Tie score (anagram)" , "Abstruse; secret" , "Inner - secret" .)