Not repeated in the initiation ceremony (4)
I believe the answer is:
once
'not repeated' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes mean the same thing.
'in the initiation ceremony' is the wordplay.
'in' says the answer is hidden in the clue.
'ONCE' can be found hidden inside 'initiation ceremony'.
Can you help me to learn more?
(Other definitions for once that I've seen before include "In former times" , "Cone (anag.)" , "On a single (or past) occasion" , "At a previous time" , "Sometime" .)