Crossword Genius

Room to accommodate Arab's Catholic belief (8)

Ross

I believe the answer is:

romanism

I'm a little stuck... Click here to teach me more about this clue!

'catholic belief' is the definition.
'Romanism' can be an answer for 'belief' (Romanism is an example). I am unsure of the 'catholic' bit.

'room to accommodate arab's' is the wordplay.
'room' becomes 'rm' (abbreviation).
'to accommodate' means one lot of letters goes inside another.
'arab's' becomes 'Omani's' (someone from Oman).
'rm' enclosing 'omanis' is 'ROMANISM'.

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I've seen this clue in The Guardian.
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