aecidium

is likely misspelled.

has no English definition.

As a noun aecidium

is the cupulate fruiting body borne upon the mycelium of certain fungi commonly parasitic upon specimens of the Compositae, Lamiaceae, Leguminosae, and Ranunculaceae families.

As nouns the difference between aecidium and cecidium

is that aecidium is the cupulate fruiting body borne upon the mycelium of certain fungi commonly parasitic upon specimens of the Compositae, Lamiaceae, Leguminosae, and Ranunculaceae families while cecidium is a gall produced on a plant by infection from insects etc.

As a proper noun aecidium

is .

As a noun ascidium is

(botany) a pitcher-shaped or flask-shaped organ or appendage of a plant.