Impressions of corresponding significance (6)

I believe the answer is:

stamps

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'impressions' is the definition.
(I know this)

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

(Other definitions for stamps that I've seen before include "Philatelists collect them" , "Tramples" , "Philatelist's interest" , "creates an impression" , "Puts the foot down on letters" .)

I've seen this clue in The Irish News.

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