Definition of Toxin

Toxin: One of a number of poisons produced by certain plants, animals, and bacteria.

The term "toxin" is frequently used to refer specifically to a particular protein produced by some higher plants, animals and pathogenic (disease-causing) bacteria. A toxin typically has a high molecular weight (as compared to a simple chemical poison), is antigenic (elicits an antibody response), and is highly poisonous to living creatures.

The word "toxin" comes from the Greek "toxikon" = arrow poison and was introduced to medicine in 1888 by the Berlin physician Ludwig Brieger (1849-1909) as a name for poisons made by infectious agents.