Possible Clues:

• Poisonous plant
• Poisonous weed
• Toxic plant in the carrot family
• Socrates' undoing
• Drug source for ancient executions
• This man pretended to protect source of lethally poisonous drug
• Socrates' final quaff
• Canadian Evergreen
• Poison killing Socrates
• Highly poisonous relative of parsley