Large box capable of expansion (5)

I believe the answer is:

chest

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'large box' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for chest that I've seen before include "It's enclosed by the ribs" , "Trunk or crate" , "Strongbox; sternum" , "Bra on it" , "ark" .)

I've seen this clue in the Evening Standard.

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