gateway drug: a habit-forming drug that is not addictive but its use may lead to the use of other addictive drugs
drug of abuse: a drug that is taken for nonmedicinal reasons (usually for mind-altering effects); drug abuse can lead to physical and mental damage and (with some substances) dependence and addiction
knight: originally a person of noble birth trained to arms and chivalry; today in Great Britain a person honored by the sovereign for personal merit