From New Latin aecidium, the diminutive form of Ancient Greek αἰκία (aikía, “injury”). However Merriam-Webster takes the origin from the Greek οικιδιον and refers to the botanist John Hill, in his A General Natural History, or New and Accurate Descriptions of the Animals, Vegetables, and Minerals, of the Different Parts of the World, vol. II, A History of Plants (London: Printed for Thomas Osborne, 1751), p. 64: "We have called this genus, distinguished by its peculiar cells, Æcidium, from the Greek οικιδιον, cellula."
- The cupulate fruiting body borne upon the mycelium of certain fungi commonly parasitic upon specimens of the Compositae, Lamiaceae, Leguminosae, and Ranunculaceae families
- (mycology) A member of the form genus Aecidium.