Smoker's leaf (7)
I believe the answer is:
tobacco
'smoker's leaf' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tobacco that I've seen before include "Nicotine plant imported by Sir Walter Raleigh" , "Eg, shag or snuff" , "Controversial plant grown commercially" , "plugs, perhaps" , "20 [CASTRO] 's favourite leaves" .)