n. 1.  A small knotlike protuberance. 2.  Medicine   A small, abnormal but usually benign mass of tissue, as on the thyroid gland, in the lung, or under the skin. 3.  Botany   A small knoblike outgrowth, especially one on the roots of a leguminous plant that contains bacteria that fix nitrogen. 4.  Mineralogy   A small rounded lump of a mineral or mixture of minerals, usually harder than the surrounding rock or sediment. [Middle English, from Latin nōdulus, diminutive of nōdus, knot; see  ned- in the Appendix of Indo-European roots.] nodu·lar (nŏjə-lər),  nodu·lose′ (-lōs′),  nodu·lous (-ləs) adj.  | 
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