: a small mass of rounded or irregular shape: as a: a small abnormal knobby bodily protuberance (as a tumorous growth or a calcification near an arthritic joint) b: the nodulus of the cerebellum
In geology, a rounded mineral concretion that is distinct from, and may be separated from, the formation in which it occurs. Nodules usually are elongated and have a knobby irregular surface; they are generally oriented parallel to the bedding. Chert and flint, clay ironstone, and phosphorites commonly occur as nodules. Manganese-rich nodules are found on the ocean floor.