u·re·din·i·um 
(y
r
′ĭ-d
ĭn
ē-
əm) also
u·re·di·um (y
-r
ēd
ē-
əm)
n. pl. u·re·din·i·a (-d
ĭn
ē-
ə) also
u·re·di·a (-d
ē-
ə)
A reddish pustulelike structure that is formed in the tissue of a plant infected by a rust fungus and produces urediniospores.
[New Latin ūrēdinium, from Latin ūrēdō, ūrēdin-, blight, from ūrere, to burn.]