Coarse nicotine contains poison (7)
I believe the answer is:
arsenic
'poison' is the definition.
(arsenic can be used as a poison)
'coarse nicotine contains' is the wordplay.
'contains' says the answer is hidden in the clue.
'ARSENIC' can be found hidden inside 'coarse nicotine'.
(Other definitions for arsenic that I've seen before include ", it goes with old lace" , "Poisons in scare" , "Famous stage comedy ''. . . . . . . and Old Lace''" , "Ratsbane" , "Powerful poison" .)