Kind of collection to impress (5)
I believe the answer is:
stamp
I believe this is a triple definition!
'kind' is the first definition.
(I've seen this before)
'of' acts as a link.
'collection' is the second definition.
(stamp collection is a kind of collection)
'to' is a link.
'impress' is the third definition.
(I know that stamp is a more specific form of the action impress)
(Other definitions for stamp that I've seen before include "Tread heavily (on an envelope?)" , "Validation for a letter - tread heavily" , "Frank" , "Seal" , "Imprint, brand" .)