Evidence of admission (4)
I believe the answer is:
stub
'evidence of admission' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stub that I've seen before include "End of cigarette or counterfoil of cheque" , "Ticket counterfoil" , "what smoker drops in street?" , "Short piece left over" , "Pencil/cigarette remnant" .)