Tobacco in tin used up (5)
I believe the answer is:
snout
'tobacco' is the definition.
(snout can informally mean tobacco)
'tin used up' is the wordplay.
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'used up' becomes 'out' (to be out of something is to have used it all up).
'sn'+'out'='SNOUT'
'in' is the link.
(Other definitions for snout that I've seen before include "nose of pig" , "Nose; tobacco (slang)" , "Schnozzle" , "Nose and mouth of a mammal" , "Pig's nose" .)