Pathogen
WordNet
noun
(1) Any disease-producing agent (especially a virus or bacterium or other microorganism)
WiktionaryText
Etymology
From < (see ) + .
Noun
- 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.