Knowing number has come up, moment appearing endless (7)
I believe the answer is:
gnostic
'knowing' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for gnostic that I've seen before include "Relating to mystical knowledge" , "Occult" , "Having special mystical knowledge, costing a lot" .)