Paper and tobacco used in plant (7)
I believe the answer is:
ragweed
'in plant' is the definition.
'ragweed' can be an answer for 'plant' (I have seen 'Allergenic plant' mean 'ragweed' so perhaps 'plant' could also mean 'ragweed'). I'm not sure about the 'in' bit.
'paper and tobacco' is the wordplay.
'paper' becomes 'rag' (rag can mean a newspaper).
'and' says to put letters next to each other.
'tobacco' becomes 'weed' (I can't justify this - if you can you should believe this answer much more).
'rag'+'weed'='RAGWEED'
'used' is the link.
Can you help me to learn more?
(Other definitions for ragweed that I've seen before include "Allergenic plant" , "Threat to horses" , "Unwanted plant with yellow flowers" , "Plant of daisy family" , "bloomer" .)