Secret lock uncovered by sect (6)
I believe the answer is:
occult
'secret' is the definition.
(synonyms)
'lock uncovered by sect' is the wordplay.
'uncovered' says to take the centre.
'by' means one lot of letters go next to another.
'sect' becomes 'cult' (I've seen this before).
The central letters of 'lock' are 'oc'.
'oc'+'cult'='OCCULT'
(Other definitions for occult that I've seen before include "Involving magical powers" , "Mystical, involving the supernatural" , "Secret - mysterious" , "Beyond ordinary understanding; difficult to see" , "Secret, esoteric" .)