Possibly cracked container (4)

I believe the answer is:

safe

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'container' is the definition.
(safe is a kind of container)

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

(Other definitions for safe that I've seen before include "Reliable" , "Metal box for storing valuables in" , "Place for keeping valuables" , "Unharmed" , "Metal container for valuables" .)

I've seen this clue in the Evening Standard.

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