Form of worship adopted by spiritualists (6)

I believe the answer is:

ritual

'form of worship' is the definition.
(thesaurus)

'adopted by spiritualists' is the wordplay.
'adopted by' indicates a hidden word.
'RITUAL' can be found hidden inside 'spiritualists'.

(Other definitions for ritual that I've seen before include "Code of ceremonies" , "Habits" , "Customary observance or practice" , "Codified ceremony" , "Stereotyped behaviour" .)

I've seen this clue in The Independent.

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