Arkwright almost reserving room for girl (5)

I believe the answer is:

norma

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'for girl' is the definition.

I don't understand how the remainder of the clue works.

(Other definitions for norma that I've seen before include "Opera - ex-PM's wife" , "name for Monroe" , "Marilyn was properly one" , "Shearer or Major" , "The 'Rule' constellation" .)

I've seen this clue in The Sun, The Independent and The Times.

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