nodule

noun

• 1a small swelling or aggregation of cells in the body, especially an abnormal one: the area feels firm but has irregular nodules which can be painful to touch laparotomy showed white nodules in the liver
• (usually root nodule) a swelling on a root of a leguminous plant, containing nitrogen-fixing bacteria.

• 2a small rounded lump of matter distinct from its surroundings, e.g. of flint in chalk, carbon in cast iron, or a mineral on the seabed: flint nodules in the coal pits nodules of iron ore were mined