wildfire

noun

1. a highly flammable composition, as Greek fire, difficult to extinguish when ignited, formerly used in warfare.
2. any large fire that spreads rapidly and is hard to extinguish.
3. sheet lightning, unaccompanied by thunder.
4. the ignis fatuus or a similar light.
5. Plant Pathology. a disease of tobacco and soybeans, characterized by brown, necrotic spots, each surrounded by a yellow band, on the leaves and caused by a bacterium, Pseudomonas tabaci.
6. Pathology Obsolete. erysipelas or some similar disease.