an organic substance found in plants that often has toxic effects on animals.
Substances found in plants, many having powerful pharmacologic action, and characterized by content of nitrogen and the property of combining with acids to form 
Organic nitrogenous bases. Many alkaloids of medical importance occur in the animal and vegetable kingdoms, and some have been synthesised. ... (12 Dec 1998) ... 
Alkaloids are compounds containing nitrogen in a heterocyclic ring, usually derived from amino acids. It is present in almost all vascular plants. 
One of a large group of organic base substances found in plants. These substances often have toxic effects on animals.
Bitter-tasting compounds found in many plants, especially in the nightshade family (Solanaceae).