aecidium

From New Latin aecidium, the diminutive form of Ancient Greek αἰκίᾱ (aikíā, “injury”). However Merriam-Webster takes the origin from Ancient Greek οἰκίδιον (oikídion) 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." Compare also many other fungal spore-related terms in -idium, most coined after this one.