prognosticate vs guess

prognosticate is not a noun while guess is a noun.

Word	Noun	Adjective	Verb	Adverb
prognosticate	No	No	Yes	No
guess	Yes	No	Yes	No

As verbs, guess is a hypernym of prognosticate; that is, guess is a word with a broader meaning than prognosticate:

Other hypernyms of prognosticate include hazard, pretend, venture.

prognosticate (noun)	guess (noun)
	an estimate based on little or no information
	a message expressing an opinion based on incomplete evidence

prognosticate (verb)	guess (verb)
make a prediction about; tell in advance	expect, believe, or suppose
indicate, as with a sign or an omen	judge tentatively or form an estimate of (quantities or time)
	guess correctly; solve by guessing
	put forward, of a guess, in spite of possible refutation