Definition of oidium
plural -ia
play
\ō-ˈi-dē-ə\
1 a
: any of a genus (Oidium of the family Moniliaceae) of imperfect fungi many of which are now considered to be conidial stages of various powdery mildews
b
: one of the small conidia borne in chains by various fungi (such as an oidium) — called also
arthrospore
2
: a powdery mildew especially of grapes caused by an oidium
