Break into a secret passage (6)

I believe the answer is:

decode

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'break' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for decode that I've seen before include "Penetrate or solve encrypted message" , "Explain" , "Unscramble" , "Find hidden meaning" , "Do translation" .)

I've seen this clue in The Globe and Mail.

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