Source : Webster's Revised Unabridged Dictionary (1913)

Nodule \Nod"ule\, n. [L. nodulus, dim. of nodus knot: cf. F.
   nodule.]
   A rounded mass or irregular shape; a little knot or lump.

Source : WordNet®

nodule
     n 1: a small node
     2: small rounded wartlike protuberance on a plant [syn: {tubercle}]
     3: (mineralogy) a small rounded lump of mineral substance
        (usually harder than the surrounding rock or sediment)