Postage label (5)
I believe the answer is:
stamp
'postage label' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for stamp that I've seen before include "Bring foot down hard" , "Impress; postage sticker" , "put one's foot down hard" , "Validation for a letter - tread heavily" , "making an impression?" .)