speculate vs cogitate

speculate and cogitate both are verbs.

Word	Noun	Adjective	Verb	Adverb
speculate	No	No	Yes	No
cogitate	No	No	Yes	No

As verbs, cogitate is a hypernym of speculate; that is, cogitate is a word with a broader meaning than speculate:

speculate: reflect deeply on a subject
cogitate: use or exercise the mind or one's power of reason in order to make inferences, decisions, or arrive at a solution or judgments

Other hypernyms of speculate include cerebrate, think.

As verbs, cogitate is a hyponym of speculate; that is, cogitate is a word with a more specific, narrower meaning than speculate:

speculate: reflect deeply on a subject
cogitate: consider carefully and deeply; reflect upon; turn over in one's mind

Other hyponyms of speculate include premeditate, theologise, theologize, introspect, bethink, question, wonder, puzzle, consider, study.

speculate (verb)	cogitate (verb)
reflect deeply on a subject	use or exercise the mind or one's power of reason in order to make inferences, decisions, or arrive at a solution or judgments
to believe especially on uncertain or tentative grounds	consider carefully and deeply; reflect upon; turn over in one's mind
talk over conjecturally, or review in an idle or casual way and with an element of doubt or without sufficient reason to reach a conclusion
invest at a risk