ruminator vs thinker

ruminator and thinker both are nouns.

Word	Noun	Adjective	Verb	Adverb
ruminator	Yes	No	No	No
thinker	Yes	No	No	No

As nouns, thinker is a hypernym of ruminator; that is, thinker is a word with a broader meaning than ruminator:

ruminator: a reflective thinker characterized by quiet contemplation
thinker: someone who exercises the mind (usually in an effort to reach a decision)

ruminator (noun)	thinker (noun)
a reflective thinker characterized by quiet contemplation	an important intellectual
	someone who exercises the mind (usually in an effort to reach a decision)