Poison ___ (plant) (3)
I believe the answer is:
ivy
'poison plant' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ivy that I've seen before include "Climbing plant, associated with holly" , "Song: 'Poison --'" , "Evergreen creeping plant" , "With holly, it's seasonally decorative" , "Woody climber" .)