geode vs nodule

geode and nodule both are nouns.

Word	Noun	Adjective	Verb	Adverb
geode	Yes	No	No	No
nodule	Yes	No	No	No

As nouns, nodule is a hypernym of geode; that is, nodule is a word with a broader meaning than geode:

geode: (mineralogy) a hollow rock or nodule with the cavity usually lined with crystals
nodule: (mineralogy) a small rounded lump of mineral substance (usually harder than the surrounding rock or sediment)

geode (noun)	nodule (noun)
(mineralogy) a hollow rock or nodule with the cavity usually lined with crystals	a small node
	(mineralogy) a small rounded lump of mineral substance (usually harder than the surrounding rock or sediment)
	small rounded wartlike protuberance on a plant