File one used to break out of trap (5)

I believe the answer is:

queue

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

I don't understand the remainder of the clue.

(Other definitions for queue that I've seen before include "Form a line" , "Pigtail; get in line" , "Stand in line" , "Tailback" , "Buyers' line" .)

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