introspection vs rumination

introspection and rumination both are nouns.

Word	Noun	Adjective	Verb	Adverb
introspection	Yes	No	No	No
rumination	Yes	No	No	No

As nouns, rumination is a hypernym of introspection; that is, rumination is a word with a broader meaning than introspection:

introspection: the contemplation of your own thoughts and desires and conduct
rumination: a calm, lengthy, intent consideration

Other hypernyms of introspection include contemplation, musing, reflection, reflexion, thoughtfulness.

introspection (noun)	rumination (noun)
the contemplation of your own thoughts and desires and conduct	regurgitation of small amounts of food; seen in some infants after feeding
	(of ruminants) chewing (the cud)
	a calm, lengthy, intent consideration