1rare Any fungus of the former genus of pathogenic fungi, Aecidium, now known to represent the aecial stage (anamorph) of rusts of the genus Puccinia and other members of the order Uredinales. Also (in form Aecidium): the genus itself.
2Originally: an aecium. In later use: specifically one which is cup-shaped and which is enclosed within a protective membrane.
Mid 18th century; earliest use found in John Hill (bap. 1714, d. 1775), physician and actor. In some forms from scientific Latin Aecidium, former genus name (J. HillGen. Nat. Hist II. 64), originating as a misprint for Oecidium.