Share option arranged outright (7)

I believe the answer is:

portion

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

'share' is the definition.
(I know that share can be written as portion)

I can't explain the remainder of the clue.

(Other definitions for portion that I've seen before include "Serving" , "Segment" , "Helping - fate" , "Piece of a whole" , "Share, helping" .)

I've seen this clue in the Evening Standard.

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