Tool box? (4)

I believe the answer is:

file

I believe this clue is a double definition.

'tool' is the first definition.
(file is a kind of tool)

'box?' is the second definition.
(thesaurus)

(Other definitions for file that I've seen before include "Smoothing tool; organised data" , "Set of papers" , "Cutting tool or line of people" , "Line of people, one behind the other" , "Tool for sawing through metal" .)

I've seen this clue in The Washington Post, The Washington Post Sunday, the L.A. Times Daily and The Independent.

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