(Bot.) An American plant (Nicotiana Tabacum) of the Nightshade family, much used for smoking and chewing, and as snuff. As a medicine, it is narcotic, emetic, and cathartic. Tobacco has a strong, peculiar smell, and an acrid taste. Note: The name is extended to other species of the genus, and to some unrelated plants, as Indian tobacco (Nicotiana rustica, and also Lobelia inflata), mountain tobacco (Arnica montana), and Shiraz tobacco (Nicotiana Persica).