/ˈpaTHəjən/ /-ˌjen/
Noun, pl. pathogens
1. An infectious agent (colloquially known as a germ); a microorganism—in the widest sense, such as a virus, bacterium, prion, or fungus—that causes disease in its host. The host may be an animal (including humans), a plant, or even another microorganism. (wikipedia.org)
2. Any organism or substance, especially a microorganism, capable of causing disease, such as bacteria, viruses, protozoa or fungi. Microorganisms are not considered to be pathogenic until they have reached a population size that is large enough to cause disease. (wiktionary.org)
3. A specific causative agent (as a bacterium or virus) of disease. (merriam-webster.com)
4. An agent causing disease or illness to its host, such as an organism or infectious particle capable of producing a disease in another organism. (biology-online.org)
Syn: infectious agent, germ
Word origin: From Greek pathos, “suffering,emotion” + gene, “to give birth to.”