Mysterious officer commanding a sect (6)

I believe the answer is:

occult

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'mysterious' is the definition.
(I've seen this before)

'officer commanding a sect' is the wordplay.
'officer commanding' becomes 'oc' (this might be a standard abbreviation of which I'm unaware).
'a sect' becomes 'cult' (I've seen this before).
'oc'+'cult'='OCCULT'

Can you help me to learn more?

(Other definitions for occult that I've seen before include "Secret - mysterious" , "Mystical (black arts)" , "Supernatural practices" , "Esoteric, magical" , "Characteristic of supernatural phenomena" .)

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