|a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.|
|a screen or mat covered with a dark material for shielding a camera lens from excess light or glare.|
in fungi (kingdom Fungi), a single-celled asexual spore (arthrospore) produced by fragmentation of fungal filaments (hyphae) in lower fungi; the asexual stage of Erysiphaceae (powdery mildew fungi); or, in Basidiomycota, both an asexual spore (microconidium) and a male cell (spermatium).
Learn more about oidium with a free trial on Britannica.com.