Is the brother of Cain, nominally! (6)

I believe the answer is:

isabel

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'is the brother of cain nominally' is the definition.
I can't tell whether this defines the answer.

'is the brother of cain' is the wordplay.
'the brother of cain' becomes 'abel' (I've seen this before).
'is'+'abel'='ISABEL'

Can you help me to learn more?

(Other definitions for isabel that I've seen before include "Abseil with confused girl" , "Girl's name" , "Drab" , "- Allende, Chilean novelist" , "Miss" .)

I've seen this clue in the Evening Standard.

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