cogitation vs rumination

cogitation and rumination both are nouns.

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

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

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

cogitation (noun)	rumination (noun)
attentive consideration and meditation	regurgitation of small amounts of food; seen in some infants after feeding
a carefully considered thought about something	(of ruminants) chewing (the cud)
	a calm, lengthy, intent consideration