Portion of pie, a bit nice (5)

I believe the answer is:

piece

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'portion' is the definition.
(I know that piece is a type of portion)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for piece that I've seen before include "king or queen?" , "A part of something" , "rook, perhaps" , "See 3" , "that may follow show after work party?" .)

I've seen this clue in the Evening Standard.

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